Sydney Observatory needs your help.

[GOTO]

Hello everyone,

Geoff from Sydney Observatory here. We presently use a 16inch Meade LX200 for our public tours. It is purely for visual use. We are looking for a larger replacement but there are a few issues:

1. We don't want a German fork mount because of counterweight arm risks, ie head-butting the weights in the darkened dome. So a fork mount is preferable.

2. We can't have a Newtonian due to the height of the eyepiece.

3. It can't be a custom made one off.

4. We want a turn key solution.

So, the only option so far, other than a new 16inch, looks like a 17-20inch Planewave on a Mathis Instrument mount. Yes we know these are imaging telescopes. Despite the short focal length and huge secondary we haven't found anything else with the eyepiece in the right position, a big aperture and on a fork mount.

However one significant issue. We haven't been able to LOOK through one yet! Does anyone here have access to a large Planewave that would be willing to let our management team LOOK through it please? We are willing to travel anywhere and would appreciate your help. You can contact me here or via email at geoffw@phm.gov.au

Conversely, if anyone has a brilliant different approach please don't be shy but remember we need the bigger aperture to try and get down to the bottom of Mag 10 from Sydney's CBD, it must be visual and we don't want to use a ladder.

Kind regards and thanks for your help.
Geoff

[bert]

Sent private message.

Brett

[sally1jack]

I know you have said no newt , but have you look at the new faster mirrors being produce now which will give no ladder viewing for a 20 inch dob , i know Mike lockwood produces very fine mirrors at these f ratio's.If you talked to Peter Read at SDM he would be able to give you some useful information about this.
just a thought
phil

[mental4astro]

A larger aperture with a fast f/ratio won't help you. It will actually make things worse.

While looking into a scope is nice, the only alternative you have for live viewing is with a video camera. Not only will it show mag 10, but fainter too in the CBD with the 16". It will also overcome the problem that most novices don't know how to look into an eyepiece, & are also expecting to see things as they do in photographs. Even if you could see a mag 10 object in your scope, the image will be very, very faint, washed out & overwhelmingly underwhelming to novice eyes.

I'm speaking from experience here. I help out at frequent star parties at Randwick Girls' High, & the only way a galaxy is visible to their inexperienced eyes is with a video camera. Even using my 17.5", unless you know what to look for, you just won't see anything.

I use a video camera on my 30 year old C8, & not only can I see colour in Eta Carina, but I've also managed mag12 globular clusters in the LMC, all from Ranrwick.

It's not cheating - it is really the only way to overcome your problem of light pollution. Plus, it doesn't depend on a moonless night, the room doesn't need to be in the dark ( boon for insurance) and a whole room can view at the same time. As the scope slews, you see this on the screen. As air currents influence seeing you see this too. And it overcomes the issue of novices not being able to see things at the eyepiece.

You will also be able to increase the numbers of people who can view "through" the telescope to just about 100% as those who have mobility problems won't be left out because they can't see into the eyepiece.

Again, it's not cheating. It's using the right tools to overcome an insurmountable problem that will only get worse. The video camera will be able to be productive even after a 20" scope has been rendered useless from light pollution with just the 16" still being used. This aspect of not needing to get a more expensive scope with a short working life should appeal. The existing infrustructure remains, thus avoiding any expensive upgrade or costly down time - it will be functional straight away.

I'd be happy to bring my camera to give you a demo on the 16". This is the only way that you will see how effective it is. Just drop me a PM. All that's needed is a power point. There is now also a transmitter that connects to the camera to make the whole thing wireless for you.

Visual astronomy is no longer an option with DSO's for you. But a video camera will overcome this for a longer time than any bigger scope can do for you, and will open astronomy to a wider audience leaving more $$$ in your tills.

Alex.

[Wavytone]

Hi Geoff,

Appreciate the issues with safety risks with respect to things that people can bump into in the dark, or fall off (ladders).

As Alex pointed out, in the city a fast focal ratio is not a good idea as it increases the brightness of the background sky glow - you're much better off sticking with f/10 or even f/15 (as in the scope I use, which is a f/15 maksutov) and that means cassegrain optics, not a Newtonian, to keep the physical size compact.

Since this is a visual scope, the solution I'd suggest is a Nasmyth-Cassegrain, on an altazimuth fork mount. Essentially it's a Cassegrain with a diagonal flat mirror in front of the primary mirror arranged so that the light beam comes out co-axially through the altitude axis of the mount. See
http://en.wikipedia.org/wiki/Nasmyth_telescope or
http://www.millseyspages.com/astro_pages/la_palma/nasmyth.html
http://www2.l-3com.com/ios/pdf/1meter_low-res.pdf


The beauty of this is that the eyepiece is always in the same place no matter where the scope is pointing. On a large scope with a permanent mount, the fork will be sturdy enough that you can easily fit a "tractor seat" on the side of the fork so the observer can sit, riding on the fork to look through it.

Finding someone to make this configuration is going to be difficult as it will be a custom one-off.

The focal ratio is a big issue.

As Alex pointed out, a fast f/ratio increases the sky background for extended objects (nebulae, galaxies, comets) which is not helpful.You can use higher magnification to reduce the background glow, but this implies the scope should have had a longer focal ratio in the first place, say f/10 or f/12 - which would be my choice.

As you know from the Planewave example to make an f/6.7 Cassegrain the secondary obstruction is huge - the Planewave scope is intended for imaging, and it will be really bad for visual use - you will notice a big black blob floating in the centre of the eyepiece. For visual you really want f/10 to f/12, and a smaller secondary < 30% of the primary aperture.

One way to get around the constraints of a cassegrain is to build a Mersenne or relay telescope where the cassegrain focus is in front of the primary and a positive relay lens is used to bring the focal plane out where it can be reached. This permits a fast compact cassegrain (f/6 is possible) while keeping the secondary obstruction small at 25%, and the final f/ratio can be varied from say f/6 to f/15 by moving the relay lens much like a zoom camera lens. It's the same principle as eyepiece projection.

With increasing aperture at a constant f/ratio, the focal length must also be increased so the useful magnifications provided by your eyepieces will increase, too. The downside with that is that the seeing at observatory hill isn't great due to atmospheric turbulence created by the surrounding buildings and the effects on what you see will be worse with a bigger scope than a smaller one.

[h0ughy]

I agree use the 16" but with something like a lodestar - very sensitive small and save some money to boot. then could show to more at once "live"

[lacad01]

Or even a Mallincam Extreme

[Satchmo]

This piece suggests that Peter is endorsing these kind of mirrors. Peter Read has never looked through a scope with a ultra- fast mirror. He is building a few where customers like yourself are supplying their (F2.8 - F3 ? )optics by buying from the optician directly. Please correct me if I have this wrong.

The balance point no more than a few feet off the ground would not suit Sydney Observatories application of looking out of a traditional dome.

[sally1jack]

That would be correct Mark& i can see how it would not suit in this situation, i think at f3.3 20 inch can be no ladder viewing i may be wrong, i didn't intend to imply that Peter was endorsing these fast scopes & am sorry to anyone who thought i was , it was just a suggestion, i know Peter has tested f3.3 mirrors at you place with good outcomes
phil

[Wavytone]

I've had a 12.5" f/3.7... It was an interesting experiment but I wouldn't recommend such fast mirrors to anyone aiming to use it as a Newtonian - only useful for a classical cassegrain. An altaz 20" Nasmyth equipped with encoders and GOTO electronics would be quite a nice scope. With a small secondary there should be no issues designing one for f/12 and f/8 might be achievable.

[sally1jack]

It's not fast ratio that is the problem it 's the skill of the optician or lack of that give fast mirrors a bad reputation

[Wavytone]

Actually, no. The mirror had an excellent figure. The problems were:

a) huge secondary mirror - so big that in many eyepieces you see a big black blob swimming in the FoV;

b) range of useful magnification was very limited, largely due to the limitations with suitable eyepieces - many eyepieces won't work well with mirrors this fast, even now.

c) coma and field curvature (at the time I had this, correctors didn't exist) which were a big problem with most eyepieces except the Pretoria.

d) the fact that the fast f/ratio raises the background sky brightness, which basically defeats the point of a larger scope for looking at extended objects (nebulae, galaxies) in average skies. In really good sites with the darkest of sky, this might not be a problem but even in the Blue Mountains west of Sydney it was evident that f/5 - f/7 would have been a much better choice.

In the heart of Sydney the sky glow is much worse - and at Observatory Hill the naked-eye visual limiting magnitude is about 2.5. An f/3 mirror is about the worst possible choice.

[icytailmark]

In the middle of Sydney your not gunna be able to see many DSO's anyways from all the light pollution. Your really limited to planets,bright nebulas, and star clusters. You don't need over 16" telescope to view them. I have a Celestron c14 and im south of Sydney. Visually i can only see planets,bright nebulas, bright galaxies and star clusters. I have found that you cant even view the bright galaxies unless you have really good night (which is rare in Sydney) :(

[Satchmo]

Hi Phil
Its not about ladder free viewing. The dome slit at Sydney observatory would probably be chest height at the base so a Dob would be vignetted by the slit at lower altitudes. A 20" F3.3 would have you seated or knealing at 45 degree elevation- not suitable to standing crowds.

I assumed by Ultra fast you meant F2.8 to F3 . I haven't tested any F3.3 mirrors. We tested a 22" F3.6 that had been made by another vendor and refigured.

Contact me PM if you need any more info.

[Satchmo]

Most of these objections are no longer valid.

A Newtonian is clearly not suitable for Sydney Observatory due to logistics of crowd needing more constant height eyepiece and dome slit height considerations !

Any further debate about Newtonians is a hijack of the thread - I do apologise for this diversion.


I've started a new thread if anyone would like to debate Newtonians further ?

PS - Guys - apparent sky background is a function of magnification and has nothing to do with F ratio !

[Barrykgerdes]

I think the discussion has drifted a little from the help request.
I have not been to the observatory for many years but what they require will be a replacement for their old LX200 16" Meade that has given service for many years (since Halley's comet) and now cannot be repaired due to no parts for the electronics system.

It is mounted in the dome on a pier that gives suitable access to the general public to view items through the eyepiece. It did at one time have a C5 telescope as a piggy back that was connected to a Meade 416 CCD. This I assume has long been upgraded but they probably will still need something similar.

I would expect that something in the 16-20 inch planewave area with manual viewing available along with the computerised viewing costing lots of dollars and someone to baby it every viewing night will be required.

I don't know of anyone at the moment who possesses such an instrument for evaluation to help Geoff out.

Barry

[Peter.M]

I have no experience with larger telescopes, or much visual observation for that matter, But you could also consider RCOS telescopes.

[tlgerdes]

Also, as stated as this is visual, part of the appeal for people is actually looking through a telescope. Putting a camera and displaying it on a screen, may as well go and look at Youtube.

For most people who visit the observatory this is their first time seeing a telescope let alone looking through so the "theatrics" of the experience are very important.

[mental4astro]

I disagree with you Trevor.

It comes down to actually seeing something in the middle of Sydney or not in this case.

But, you also flippantly mention YouTube. A couple of years back I volunteered to show the night sky to kids in NSW's only kids palliative hospital. I took my modest little C5 & my 17.5" dob, along with a modified webcam just on a hunch I had. I did not even assemble the dob that night. What that little webcam & C5 showed those no YouTube clip can replace. Those kids had no hope in hell of looking into an eyepiece. You tell those kids that they were ripped off when they saw Saturn come into view, the image shaking slowing coming to a standstill. Tell them they may as well look at a DVD when we were able to slew the camera to different parts of the moon. The thrill these kids had that night of actually seeing a scope, even a little C5, tell them to go see a YouTube clip. Tell them their experience was a fraudulent one. After what I experienced that night, I have never questioned the legitimacy, value & power of a video camera as useful tool in astronomy.

One's experience at a telescope is not cheapened if a camera is needed. Folks are smart enough to understand what a live image is. It is not ripping them of if this is the only way to show them a galaxy. As things stand now at Onservatory Hill, you have no chance in appreciating any galaxy, let lone the full expanse of M42, or even Omega Centauri to what it can really offer. To say otherwise is not understanding the situation of both the observatory & its night sky - this, coming from a die hard visual man.

A video camera also doesn't mean no direct viewing through the scope - the Moon & planets don't require a camera. But it makes all the difference in both seeing a DSO, AND appealing to the younger generations who best relate to a monitor than an eyepiece. It is easy to forget that a novice's eyes cannot see what we can!

[Bassnut]

Exactly . Geoff came to a ASNSW meeting and explained what he wanted. Off the shelf and visual only. A pic on a screen is a daft idea, completely misses the point. I think fancy ultra wide field Is daft too, a close look at the moon beats a bunch of bright high quality dots any day :thumbsup:

[mental4astro]

No, not daft.

[Satchmo]

Hi Fred
I know you are an astrophotographer- so you've got an association in your mind with fast f ratio = wide field ? just a reminder that visual magnification on any 'scope is controlled by the eyepiece . The range of eyepeices and amplifiers with long eye relief even in short focal length eyepieces, available now , mean that no configuration of telescope is limited in any way to achieve the full range of exit pupils/magnifications needed. Sky background brightness and observed detail in the image is a function of the magnification, and has nothing to do with the F ratio of the 'scope.

[Bassnut]

awe come on, looking in an eyepeice is a completely different experience, regardless of how crappy. If I turned up just to look at a friggen screen Id walk away disappointed. Its not about what im looking at in this case, its how (for the experience Geoff is on about).

[Bassnut]

OK, fair call, sorry about that, your right of course :thumbsup:

[mental4astro]

Good, you won't be casting a shadow on my doorway then.

You're now on my ignore list mate. I've never read anything constructive come from you. It had been a while since anything had come from you, and nothing's change, and I've had enough of it. See ya!

[Barrykgerdes]

The discussion is drifting into an argument again. Have any of you been to the observatory and seen the look on the faces of the younger set (and some oldies too) when they get to look in the eyepiece of an astronomical telescope and see craters on the Moon, the red spot on Jupiter and the rings of Saturn? They don't want a picture on the TV. They want to see the actual object through the telescope. Fred and Trevor know this, They have been there.

This is what it is all about. There are suitable telescopes that Geoff knows about that fulfil his requirements but he would like to see one in operation so he can set about obtaining one.

Barry

[Poita]

Video astronomy could be a good adjunct to eyepiece use. The views are just as instant, far more satisfying and available to those with vision problems.

[brian nordstrom]

:thumbsup::thumbsup: Spot on Alexander , when I lived in Whangarei NZ building the ANZAC Frigate's for the OZ and NZ navy's I was a hard core member of the Northland astro Society ( founding member. ) and with lots of hard work , grants , members , but over the years we watched 'light pollution' :shrug: encroach on the observatory from the expanding city .
Over there we have a CG14 on Losmandy Titan , 4 steps at eyepiece to clear the OB's walls for Joe , Jane amateure atronomer's ,,,
,, amateur astronomer's , are Safe . . And about this time the C11 that gets pressed into service as a Zoom Lense 2800mm long and played on the TV screen via a Meade 'Lunar Planetary ' , where 10-15 people will watch as they stand in line to see the real thing in the C14 ( if they are lucky , ) , Wets the appitite's .
And as has been said ,,
" Peaole aint stupid "

They pay their entrance fee and get a show .

ps. Because of the the light pollution in Whangarei , 2009 , the Northland society looked at a larger locally built Cassegrain, but we to discovered that the 6inch Saxon Mak and 100mm binos gave better views in the orange haze ..
They still have the C14 and C11,
I hear you Alex.

Keep the 16 inch OTA , and look into a few new mount designs that are out there . As been said .
Brian.

[Wavytone]

Back to Geoffs original question...

I suggest that ultimately the problem to be faced is that beyond a C14 or the Meade 16", the only commercially produced large scopes are dobsonians. Anything else (cassegrain, etc) is a specialty made to order, so you can't just "go see one" and if you like it, buy another off-the-shelf.

[GOTO]

Hi all,

I really appreciate your ideas but please I did not wish to cause a fight. We have long given up on deep sky objects bar the few everyone here knows about.

Not long ago we (Powerhouse Museum) commissioned some market research and found one of the key reasons people come is to LOOK through a telescope.

My love of video astronomy led me to install a GSTAR-EX with a 300mm Nikon lens on the belly of the 16inch. The view of the two main globulars, open clusters, even the Moon and Sun was great imo but the public weren't interested. Each person wants to have his or her turn at the eyepiece. Don't forget we have a 3D theatre and planetarium to enhance the experience.

The dome walls do add a complicating factor and we are aware of the skyglow problem from the CBD. Our first government astronomer Reverend Scott knew it was not a good place to build an observatory but 155 years later we are stuck, somewhat happily I must say, as it is one of the most beautiful workplaces in the world. But I digress.

We looked into a Nasmyth without any luck and though we do have a budget, $185K is beyond it I'm afraid. Putting the 16inch onto a new mount is an option. So, this is why we would like to look through a Planewave. If the view isn't great we will return to the proverbial drawing board.

Again thanks for everyone’s input and I'm thankful for the private messages, which I will respond to shortly.

Kind regards
Geoff

[brian nordstrom]

:) Geoff , thank you .
The OTA Meade 16 inch . if The Observatory aint going to recycle it ?Where will she go? Bro?
, As a Kiwi , I dont know this LX200 16inch personally ( but I have heard of her ) , quite a few here know this scope as well , reading this cool thread .. she is moving ...
Dont GIVE her away .
Brian.

Brian.

[Satchmo]

Geoff - here is a link to the RC OPTICAL 20" RC tube.

http://www.rcopticalsystems.com/telescopes/20tube.html


I think it would be really worthwhile for someone to come along one night with a portable 20" and you can compare on site the views through a 20" at the equivalent magnifications you would be using with a Cassegrain to get some kind of idea what the public would see and you can compare in real time with the 16" . My guess is with the heavy light pollution there that the extra aperture is not going to make a substantial difference to a member of the public and certainly not on the Moon and Planets ,which are mostly seeing limited with large apertures, meaning you won't be able to exploit higher powers the extra light affords.

[AstroJunk]

Don't sell stars that faint :lol:

To be brutal, if you can't see mag 10 with the 16", then the conditions are now simply too poor. One mag deeper would require a 25" and regardless of the design (of Dob), is not going to be as swish as the Meade if you entertaining a corporate party for example.

Similar has been mentioned already: Piggyback a 100mm refractor with a colour integrating video eyepiece (choose your price point, it matters little when looking at a almost non-existent star field) and show the image on a wall monitor with the star dedication, photo and other trimmings as an overlay. At the same time try to locate the actual star within the bounds of an illuminated reticle on the 16". 99 times out of 100 the donor will 'see' the star either real or imaginary and go away happy.

When asked to show these things, many of the amateur community do the polite thing and show a 4-5 th mag Star in the rough direction of the one they bought...

[netwolf]

Gama has a CDK 20" from Planewave on a MI-750 mount.

Though I am not certain a CDK is exactly a good fit for a Visual scope, its full potential would be under used.

http://www.iceinspace.com.au/forum/showthread.php?t=40390&highlight=CDK

Another Alternative is as some one else mentioned maybe an RCOS EQ Fork, which has a relatively small foot print.
http://www.rcopticalsystems.com/mounts/rcosequatorial.html


I still recall my school visit to the Observatory and the Meade scope, I hope there is some way to keep it going. Maybe place it another Observatory in NSW. Or perhaps you could just defork the OTA and get a new Mount for it.

[mental4astro]

Geoff, I certainly agree with everyone wants to look through a scope. But in suggesting video I did not say exclusively. With a combination of both visual & video a larger scope won't be needed. A larger scope won't help short term or long.

I would also love to see a larger, state of the art scopes being used at Observatory Hill. I don't see an exclusive visual solution as the best.

[Barrykgerdes]

Refurbishing the existing early version of the 16" LX200 classic is not really an option. The main problem is the age of the electronics that drive it and they are beyond repair now. The OTA could be fitted to a new Goto fork mount but that would be no easier than getting a new updated telescope. I know because I have been involved in their repair at times. The 16" Meade has different electronics than the smaller versions and supplies of spares are now exhausted.

The Macquarie University has a similar 16" LX200 that also is getting beyond economic repair.

Regarding Dobsonian telescopes I am sure the observatory has quite a few of the various sizes of Dobsonian telescopes that are trundled out for special viewing occasions. However as Geoff says that is not what the viewers want. They want to look through the eyepiece of a telescope from inside the dome.

Barry

[tlgerdes]

As an adjunct to this, there could be a very well kept 16" LX200 OTA going for a good price soon ;) , as it is just the mount that is giving problems.

[netwolf]

Barry but could the electronics be replaced with a diffrent system.

Argo Navis with ServoCAt on LX200 Classic.
http://www.chesmontastro.org/node/7365

Sitech Servo refit of 16" LX200 classic
http://finance.groups.yahoo.com/group/SiTechservo/message/14294

AWR Goto have pictures on there site of a LX200 classic that was retrofitted.
http://www.awrtech.co.uk/ih/lx-upgr.htm

It seems to me the CDK and RCOS alterntatives would be far more expensive and would be under utilized if only used for Visual astronomy.

I am guessing if the Motors in the LX200 are still funcational and are Servo motors then it would be very easy to fit the Sitech to this. I will even donate my Sitech for testing if that woud help. I would hate to see it put out to pasture, it has so much history to it. So many people have used it.

[Wavytone]

Geoff,

So...it's back to a 16"-20" cassegrain on an altaz mount; perhaps a Nasmyth; or alternatively, taking the 16" Meade OTA and finding a new mount for it.

[Barrykgerdes]

Replied by PM

Barry

[netwolf]

Thanks Barry, I understand now.

Now the question is what modern scopes are better for Visual astronomy. The CDK and RCOS are built more for Imaging than Visual use, though they can be used visually. I have never looked through one, so cant comment. But it seems this is what is commercially available.

The alternative is to buy a Fork Equatorial mount like the MI-750 and reuse the 16" Meade OTA. Then later perhaps upgrade the OTA with something better.

MI offer 3 goto systems, Sitech, AP GTO3 and Bisuqe TCS. While I like the Sitech, i think the AP GTO system looks like the simplest to use standalone without computer. Or you could use Sitech or Bisque with SkyFI and a Skysafari on a Tablet to control it.

[rogerco]

Private reply? What is so secret? What is the answer to the suggestion that the electronics could be re-engineered. I find it strange that an electronic circuit couldn't be designed for less than the tens of thousands that a Planewave would cost. :screwy:

[Wavytone]

Probably easier to take a set of electronics made for a smaller scope (eg. the SkyWatcher Synscan) and make an interface to drive a larger mount with higher powered motors etc - or interface to an iPad/PC and forget about handsets.

Regarding sources of larger RC scopes, Planewave aren't the only ones - there's APM in Germany (Markus Ludes) making f/9 cassegrains 40-60 cm aperture with altaz fork mounts.

[netwolf]

Roger, no secret as Barry has already mentioned the electronics are quiet old. While the engineer in me thinks yes we can patch up a solution and go, we must also consider the commercial nature of this. Consider the Windows OS, sure MS could continue to Patch XP and keep it going but at some point one must just consider an overhaul to a new OS. While we may with some work be able to patch the Servo motors and make them work with a different control system, there is the question of ongoing maintenance and availability of parts. A new system whatever is decided will come with warranty and spare parts availability.
A new mount at the very least would make a more reliable system to maintain and upkeep.
From what I have googled up even those who have jerry rigged new controllers have had to tweak the motor's and encoder electronics to work with the new control systems. Eventually these electronics and motors will wear out and need replacement again. While for private use this would be no issue and Barry and I agree if it were our scope that is what we would do. But this is a Observatory that would like at the foremost reliability and up time for its many visitors. For private use we can live with some downtime, but in a commercial setting that does not work well.

Some times young over zealous engineers can learn much from the wisdom of our elders. Especially those who have actually spent a lot of time repairing such systems.
Thanks Barry.

[Barrykgerdes]

PM in this case was Phone Message to a personal friend, Fahim, and I had a long general phone conversation about some engineering work I did for him and included general information on Meade electronics that I had already spoke of in this thread.

In regard to re-engineering we are talking of a commercial decision for a one off design. I would estimate the cost in this case at well over $100000.

This thread has gone so far off geoff's original request that was for a chance to look at some potential replacements that it is hard to see what the argued suggestions have to do with the original thread topic. A commercial decision to replace the telescope has already been made.

Mark (satchmo) quite rightly started a new thread on the merits of the different telescope types for CCD viewing etc for open discussion.

Barry

[Wavytone]

There is more to this than many here suspect:

a) There are huge questions about long-term life, maintainability and supportability. An observatory instrument really is expected to last for many decades with minimal maintenance, and maintenance than can be done locally - if there are crucial proprietary bits dependent on a foreign supplier that isn't going to be around for a long time, forget it.

Commercial electronics don't last long. Even commercial telescopes don't last long - take a look at the condition of the 16" Meade, and then think about how long old clockwork museum-pieces have served, such as the 9" Oddie at Stromlo before it was destroyed by fire. And ask yourself why people will pay huge sums for classic antique old refractors in working condition. The only modern commercial scopes that look like lasting many decades are Questars, and some of you wonder why people pay the price for these.

And for something really scary, go take a look a Porter Garden Telescope in good working condition (its just a 6" Newtonian, after all) - serial #3 in working condition http://www.considine.net/mac/pgt/ sold for over $18,000 a few years ago, and a modern homage (ie reproduction) faithful to it was made recently in a small batch - they went for $59,000 http://www.astrosurf.com/re/unusual_telescopes_russell_porter.p df

Mitigating obsolescence is thus a very real problem.

b) Aesthetics. Most people expect to see a big, impressive piece of equipment which justifies the 6-figure price paid by the taxpayer (and the astronomers salary) - and with an eyepiece at the back end, something you swing at the target.

They don't expect to see a bunch of flimsy sticks that look like an overgrown bagpipe, with a mirror you mustn't sneeze at, and an eyepiece in the "wrong place" (Dobs).

c) It has to be visual. As any who have done public viewing nights, people will PAY to actually look at Jupiter through a big, impressive telescope while standing in the dark. They WILL NOT pay to watch a video or look at photos that may as well be from Youtube, or a book.

I am quite sure almost ALL OF YOU would leap at the chance to look at Jupiter visually through a big scope on a nice night.

It's no different with my paragliding hobby - people will pay $600-700 per hour to experience a tandem flight, despite most tandem flights being a boring trip to the beach below, yet most have never watched helmet videos on Youtube - even in HD and 3D it's just not the same as DOING it.

d) Visual also means it has to be safe and convenient for the public to use, in the dark. For anything bigger than the Meade 16" this virtually forces the solution to be an altaz mount, and a fork.

For any solution a human-factors study is needed, to:

- identify how the telescope is used,
- ensure a wide range of people (male and female) of varying heights and physical abilities can use it without injury,
- ensure those with disabilities can use it, within reason; and
- conduct a safety-hazard analysis to identify risks and mitigate them.

e) Maintainability and access. If it is permanently mounted it has to fit into the building, physically and structurally, and consideration given to removing major parts for maintenance (not just the optics).

With respect to the above, by way of example consider the replacement for the Oddie at Mt Stromlo - even though it long ceased to be much use at the academic level as a teaching instrument, the observatory is replacing it with a beautiful refractor, although the optics are modern it remains faithful to what the public expects of a museum-piece. And it happens to work, ie you CAN look through it.

[Barrykgerdes]

There are many references in this thread about refurbishing the Meade 16" LX200 classic. This is impractical and if you know these telescopes you will know why.

I have worked on the electronics and mechanics of the 16" LX200 and they bear little resemblance to the smaller LX200's or any of the other GOTO telescopes. I have had access to parts and maintenance data that is not available to the home maintainer, particularly replacement motherboards that have in themselves been faulty. The electronics has been upgraded a number of times to address "bugs" and the maintenance instructions are only basic. Many critical parts were over rated for the job and do not have replacements. Continued repair is just not an option.

Barry

[ausastronomer]

I seriously think there is a lot of money being aimed in the wrong direction here.

The telescopes under discussion namely Planewave DK and various RC's are imaging instruments and not the greatest for visual use, for a number of reasons based on the physics of their design.

The whole purpose is partly self defeating when one considers the prevailing sky conditions, making lunar, planetary and double stars the targets of choice. For these targets a scope like a 6" or 7" Maksutov housed in the dome would give far better visual lunar planetary views than these photographic instruments you are considering. I was in Sydney about 15 years ago one Friday night and I took my wife up there to show her the Observatory. I remember looking at Saturn through that 16" LX200, which was pretty new at the time and I can tell you the view was downright poor. I didn't announce to anyone that I actually knew what I was looking at and the view was very poor, because that would have just spoiled the enjoyment of those people who didn't know what they were looking at. My thoughts at the time, which I kept to myself and my wife were, "why did they waste all that money on this POS, when a 7" Mak would eat it on lunar/planetary views", which is all the location is really capable of supporting.

One far less costly option may be to consider a much smaller telescope housed in the dome for lunar/planetary views and then a compact large aperture dob for use in the grounds on DSO's. eg a 20"/F3.3 which adults could use without a ladder and kids would only need a small step stool to use. I can appreciate that the dome helps with light pollution but the light pollution is such that the view of DSO's is going to be poor wherever you set up the telescopes.

If you must have a big telescope in the dome you could also consider the 16" Parks HIT series. This is a 16" F4 newtonian with an F15 Classical Cassegrain focus. (http://www.parksoptical.com/site/hit.htm#7) You would only be able to use the Cassegrain focus for reasons already stated, but this will be a far better visual instrument than the Dall Kirkhams and Ritchey Chretians you are considering. Their is no free lunch. Unfortunately being a 16"/F15 telescope with a 6 metre focal length even an eyepiece like a 55mm Televue Plossl will give 110X. A 41mm Panoptic, which is as wide a FOV as you could get, will give 146X at about .46 degrees.

Cheers,
John B

[mental4astro]

Why isn't the current fork mounted Meade 16" being considered? The LX600 (http://meade.com/lx600). Yes there is the same problem of the electronics, but this will not change regardless of the solution. And as has been repeatedly mentioned, a bigger scope here is a step backwards.

The way things are going now with light pollution, it won't be long before mag 9 or even 8 will be near impossible to see. Yes, folks want to look through a scope - that goes without saying. But to give them a crappy view too isn't much chop either.

Yes, I'm on the outer here, but to offer ONLY visual without an adjunct of video in a no win situation, doesn't seem a good long term thing.

Please understand, I don't do astrophotography. I have no interest in it, I don't care for it. My intersest in astronomy is a purely visual one. But I do also care for giving novices a chance at seening something that would not be visible, and that's intelligable to them. Hmmm, are there even any eyepieces are Siding Springs?

Even if it is a piggybacked refractor (and it's a scope that novices will identify as a telescope) with a camera, it doesn't stop the visual component, but helps to also highlight the problem of light pollution too - that it isn't the scope or the objects in the sky that make for poor viewing. Like John said too, the current image is very poor because of conditions, and it won't improve with a larger instrument either, particularly one not optimised for visual use.

And I don't agree with the YouTube arguement. It's dismissive and shows little consideration for your target market. There's a distinct difference between a heavily processed image taken at a dark site to a live one from where ever you are.

If this is the way you want to do it, go for it, and I'll begrudgingly still suggest Observatory Hill to visitors. But, it's my tax money too that's being spent, so I do want to see it spent wisely, not on solutions that are not well considered. If nothing else, just NOT a larger scope that will make things worse from the very start.

[Wavytone]

All... many of you aren't listening to the simple needs Geoff has clearly stated and are instead leaping to push specific solutions that don't fit the needs and constraints that apply, by a wide margin.

The observatory is a functioning MUSEUM and IMHO we should all be quite grateful the Powerhouse museum considers it appropriate to open the observatory to the public at night and equipped with a working telescope OF ANY SORT.

Which is a lot more than can be said at Greenwich in London - the damned beancounters slashed the budget there so heavily it has NO functioning telescope at all, and has been renamed a "museum of time". The permanent exhibits have been reduced to little more than Harrison's clocks, a pathetic 3 metre GOTO portable plastic planetarium in one room, another room running a powerpoint slide-show and a gift shop that flogs badly made indian replica junk. As one who remembers what the museum used to have, it was such a shock that I had to apologise to my wife, having dragged her out to see Greenwich in appalling bad weather.

The philistines demolished the Paris observatory long ago, just a stone pillar remains in a park, rather like what's left of Parramatta observatory...

[Satchmo]

How about one of these ?

http://www.meade.com/max

$USD 35K ?


Put heavily padded vinyl sock/boot over the dec./ counterweight shaft to save anyone who bumps their head on it , and wrap the boot in red LED light strip turned down low so its presence is obvious....

[dannat]

to Alex & others - the observatory being a historc/museum type setting the telescope will be used as it would have been -via an observer looking thru the eyepiece;
same situation exists at Melbourne observatory -the general public come along to look thru the eyepiece, it adds to the exp. for them to look thru as once what an observer did, people seem happier to line up & wait a turn to look thru at saturn rather than watching it on the screen

GEoff do you have a pic of the observing rm so we can see what room there is available?
AT Melb obs we make people stay seated while we move the 8" frac on German EQ -the counterweights are substantial, & would surely knock you out if someone swung the scope quickly
in the other obs we use a 12" long f/l Newt - on a twin pier mount with steps for users to get up/down to the ep -the Newt also has a convenient rotating turret to get the ep in the best position

[mental4astro]

I get that. I really do. But without an alternative no matter the aperture you stretch things out to, the image quality will always be poor, and ultimately disappoint if humans eyes are the only tool used.

Look, it is only an alternative addition to the status quo I have put forward. But I still see no one arguing the case that one will actually see as much or more with the larger scopes originally proposed for Observatory Hill, and that they will be viable visual instruments long term.

As a die hard visual devotee of astronomy, it saddens me the situation faced at Observtory Hill. I don't care for C3PO telescope or R2D2 cameras. Nor have I mentioned any. I just want the best decision to be made with ALL alternatives given a fair hearing. Help was asked for, and it will come in many forms, and sometimes not the ones that are expected or originally considered.

All the best with Observatory Hill, Geoff. You are in one heck of a situation.

[gregbradley]

You'd be better off with a 6 to 8 inch APO than a compound scope.
Seeing is the issue with larger longer focal length scopes. Its all blurry.

My CDK17 is supposed to be good as a visual instrument. Mine is usually setup for imaging but I have looked through it two times. Yuck. Its all blurry from seeing issues. Lousy. Perhaps it would be good in great seeing at a dark site. Additionally the CDK are not well baffled (I think they may have corrected that now and they sent me a free baffle kit which I installed and have yet to test). As a result you often get light streaks from bright out of view stars. I also once had a 12.5 inch RCOS which has a large secondary obstruction (50%) and therefore optimised for imaging rather than visual - double yuck for visual. At least the CDK I have has a smallish secondary % (around 30-35%). (they recently changed the secondary mirror size to around 45% I think to make it better for imaging so even less suitable for visual with the 17 inch).

Whereas looking through a good 150 to 180mm APO - wow. APOs are known to cut through the seeing. Stars never look better than through a good APO. Next best would be a big dob but I imagine they need dark skies to excel.

For that observatory perhaps you should be looking for a nice largish APO. 6 inch APOs are often regarded as a sweet spot for APOs. But an APM 203mm might be nice. APO's probably cut through the light pollution better as well. You could put filters on the diagonal like a light pollution filter (well you could do that with any of them).

For compound scopes and visual you need a small secondary (30% say).

Takahashi Mewlons are often very highly regarded for visual as being the closest to a good APO. The Mewlon 300 is very highly regarded and is long focal length which may serve you well in bad light pollution.

So I would suggest looking for a nice big APO or a Takahashi Mewlon 300 for high impact visual.

There are many internet reviews of the Mewlon 300 and I think you'll find they are rave reviews about how great the views are. Its not great as an imaging instrument due to the small corrected circle and slow F ratio.

The best visual views I have had through many scopes have been:
1. TEC180 fluorite
2. Tak FS152
3. AP140
4. Big dobs at a dark site.
5. Celestron 11 inch go to.
Probably the FS152 had the biggest wow factor being a fluorite doublet and excellent contrast, the TEC180 is very good and the AP140 is quite a wide view but with unbleivably pinpoint stars. TEC140 hits above its aperture as well. Teh TEC180 and AP140 woul outresolve the FS152 though. I think due to the better colour correction and higher Strehl. Triplet is the way to go.

But don't expect to see galaxies from Observatory Hill unless its Cent A or Sculptor and that's about it.

Greg.

[ausastronomer]

Hi Greg,

I would agree with your recommendation of a 6" to 8" APO refractor as being telescopically the best option. However, I am not sure that the Dome configuration is conducive to using and mounting such a scope. I believe they have a need for a fork mounted scope.

Cheers,
John B

[gregbradley]

I see.

Is an APO unable to be mounted on the fork mounted scope? Is the problem how much of the scope sticks into the fork? In which case depending on how many mms that clearance is, they are limited to a scope that mostly sticks out the front with very little at the back like SCTs or CDKs.

As I say my CDK is not good for visual but that may be mostly due to the seeing not being up to handling a 3 metre focal length scope.
1200-1500mm may be the max for what the local seeing is likely to be.

Tak Mewlon may be the way to go then. I think there are a few with Mewlon 210's or 250's on this site that could comment.

Greg.

[Wavytone]

Greg,

I know of an 9" observatory refractor - and its for sale too - that fits that description - it has folded coude optics with a weighted OTA so that virtually none of it hangs below the dec axis, and the focus is brought out down the polar axis at desk height.

Ideal, in some respects.

The snag is, it's an old achromatic airspaced doublet, f/15 probably made in the 1960's from the look of the mount, so I'd bet its not coated either. The collective light losses from 4 mirrors and the uncoated doublet would be fairly bad so I didn't mention this before.

Adding a modern coated APO objective, rejigging the mirrors for a faster lens, and shortening the OTA would however blow the budget, I'm sure.

Marks suggestion re the 20" Meade Max is probably closer to the money BUT - and it's a big BUT - poses exactly the same issues as the 16" Meade does now - ie complex proprietary hardware and electronics that probably won't last 10 years - and the question of support is mighty interesting as Meade's future looks decidedly shaky. Perhaps ok for an amateur who will give it relatively light use and probably won't keep it 10 years, but its not a long term solution for observatory use.

In some respects this raises the question whether its actually cheaper over a long period - say 50+ years - to buy cheap amateur grade telescopes and consider them disposable, replacing them every 10 years to take advantage of the current technology, vs buying one considerably more expensive telescope that might last this kind of time frame.

[netwolf]

Maybe something like the one Deitmar uses 9" TMB
http://www.iceinspace.com.au/index.php?id=41,465,0,0,1,0
His images through this are amazing, also I think he uses a single Arm fork mount for this.

Actually for Visual why not a Folded Achromat might be fine.

[strongmanmike]

Having worked at the Canberra Observatory as a public explainer for 10 years between 1985 and 1996, for me, if the dome configuration can support it than I am with Greg, something like an 8" refractor on a good mount (AstroPhysics, Takahashi, Paramount etc) would not only give the best and crispest views but also look impressive and classic. Like the Sydney Observatory, the Canberra Observatory was located in a very light polluted location. The Observatory had a 7" Starfire refractor riding piggyback on a wonderful Takahashi-like 16" F5/F16 Newtonian Cassegrain on a spectacular professional grade GEM. WE almost always used this scope in Newtonian focus but while the sight of the 16" impressed people when they walked in, in the end I simply stopped showing people through it as the views under light polluted skies were very disapointing and essentially a waste of time, many people after seeing such a beast when they walked in felt robbed. The 7" Starfire however gave wonderful rewarding views of the planets, double stars and even globs and planetaries and the handful of bright galaxies available looked good too, the scope could handle high powers too so it allowed for some pleasurable variations in the viewing sessions.

I also used the late 9" Oddie refractor at Mt Stomlo Observatory on many occasions as a young man and this gave far and above the overall best views of almost everything and was probably equivalent in wow factor to about a well collimated 20" Dob. It had some focal length and just delivered in spades.

I always imagined had I ever been in the position to equip a public observatory... with a decent budget at my disposal ;) I would have gone with the largest APO refractor (on an appropriately solid mount), that the budget would allow, 8" to 10" (or larger) if possible :prey: :thumbsup:

Cheers

Mike

[Wavytone]

Hehe... I remember that 16" well, Mike... it was at the back of the Tradies Club in Dickson.

When it opened I think half of CAS were wondering WTF ? while the other half were laughing at the waste of putting a telescope like that in that awful location. I walked away shaking my head in disbelief when it opened.

After restoring its predecessor (Colonel Oddie had a 4.5" Cooke first, on a very beautiful mount which was originally used to do the site survey leading to the selection of Stromlo for an observatory), subsequently I had its big brother (the 9" Oddie at Stromlo) to myself one night a week, for several years before you. Both were great examples of what a refractor could do, and it is little wonder it is being replaced with a slightly smaller and faster APO.

The trouble is, nobody makes 'scopes like that as a "commercial off-the-shelf" item - they're all one-offs built to order. Even in Oddies day.

[strongmanmike]

Man the Oddie was just unbelievable in good seeing, one Mars opposition back in around 1998 (?) it looked like a Damien Peach photo, even my 6 year old son who was with us that night was making out all the major surface details.

I first used the Oddie in early 1984 as a 16 Yr old, my mate Attila had been using it for a year previously as part of the ACT college access (was that how you accessed it too?) including the Zeiss camera. We used the Oddie as a guide scope (http://www.pbase.com/strongmanmike2002/image/110766126/original) for our C5 and Cold Camera :P....ah, sigh...those were the days :)

Definitely a great scope for a public observatory, if you had a housing large enough of course.

Mike

[dannat]

The old 8" from 1874 still gives excel planatary & lunar views with the old Brandon eyepieces, much crisper on planets than the 12", we have it on a German EQ, but eyepiece location can be tricky, we have small steps & put the tube both over & under the mount...the public are very happy with a planet view & lunar close up, galaxies in the city are a waste iPod time, even carina neb is hopeless in Melb city, Sydney would be the same, orion is ok

[GOTO]

On behalf of the staff I would like to thank everyone for their ideas and input. Please note we have not committed to anything at this point and we have received some very good suggestions which we are following. We have no intention of wasting your money.

I will take a picture of the dome soon and put it here for you all to see.

FYI, we have several scopes including a 12inch and 16inch dobs which we trundle out every now and then for major events. I love the view they give but on busy nights, despite telling everyone that they easily out perform the north dome scope (heat from the building is another major problem), there won't be a queue for them but a massive one for the domes, why? People love the domes and the experience they bring.

Some here have mentioned the quality of the view. Optical quality is one thing but varying staff focus is perhaps a bigger more problematic issue. If anyone can suggest a fast reliable way we can standardise visual focus, again please let me know. Video is not an option as a replacement.

Overall the view through the 16inch SCT has been good for most objects. It's a solid B+ imo. Why don't we keep it? We may well do so but we are investigating options within a budget.

Again thank you for the discussion.
Kind regards
Geoff
geoffw@phm.gov.au

[gregbradley]

APM do a folded APO as well. Dietmar uses one. As I recall its 9.25 inches and will reach deep sky galaxies.

Greg.

[Barrykgerdes]

Hi Geoff
Yes focus is a problem for multiple users. When I am at astronomy nights with my scope. I have two methods.

1. I set the preliminary focus with my glasses on. This sets the start position and works for most viewers but if the viewer has noticeable thickened glasses their focus without glasses will be quite different. When there is sufficient eye relief they can usually view the standard focus with glasses on. But will always require a refocus with glasses off.

2. I have a LX200 that I fitted a mechanical counter to the focus knob. (I am lucky in that my scope has very little image shift with the standard focus knob). This allows re-setting to a standard position when the focus has been adjusted. The precicision of the scale is such that the scale even registers the difference between cold and warm focus by as many a 10 divisions. This method can be fun if you can see what glasses the observers are using. You can soon learn the offset for varying degrees of long sight and short sight by looking at the thickness of the lenses and set focus before they look into the eyepiece.

Barry

[Satchmo]

What a bizzarre thread - we go through all of this and end up with everyone agreeing a sub 10" APO would be best- when the original problem was 16" being not enough aperture ?:shrug: Perhaps if we keep discussing we can come to the conclusion that the Earth is actually flat ? :)

Refractors are not immune to the laws of physical optics - a 9" scope can never be any more than a quality 9" 'scope. I have seen a stock commercial 10" Newt trounce a 7" Starfire refractor on Jupiter as any good 10" scope should .

[gregbradley]

Don't Televue sell diopters for their eyepieces for this issue of varying focus?

Greg.

[gregbradley]

Refractors are not immune to the laws of physical optics - a 9" scope can never be any more than a quality 9" 'scope. I have seen a stock commercial 10" Newt trounce a 7" Starfire refractor on Jupiter as any good 10" scope should .[/QUOTE]


I am sure we've all had experiences with various compound scopes where they excelled. But the usual experience is its very hard for a compound scope to match unobstructed beautifully figured triplet optics.
No obstruction seems to be the big difference.

Also not everyone likes diffraction spikes. Obviously compound scopes big strength is large aperture cheaper than APO optics which are usually limited by availability of glass and difficulty of manufacture. Its a common remark that 6 inch APOs cut through the light pollution better than any other design. Perhaps that is due again to the lack of obstruction and better contrast.

Greg.

[Satchmo]

As long as you don't mind seeing even the brightest deep sky objects visually as small dim `contrasty' fuzzy blobs in a typical sized
APO. Lets call a spade a spade.....

[Wavytone]

Greg nice try but you've missed two subtle points.

Firstly, the reason smaller aperture scopes often cope better with turbulent seeing is that the dimensions of the microthermals are typically of the order of 15-40 cm. In average seeing a 10cm scope will show discernible diffraction rings and an Airy disk in conditions where a 20 cm or larger scope will just show a fuzzy blob. The atmospheric effects are easily seen if you defocus on a bright star. In daytime I've flown through this kind of turbulence at heights up to 3000 metres on my paraglider, you can feel the turbulence on your face and it makes for a bumpy ride, and it's also one of the reasons no-one likes to fly paragliders over urban areas.

The seeing on most nights at Observatory Hill is so poor that it does imply a large aperture scope is going to be unsatisfactory. A site survey to assess this quantitatively would be constructive, before making any decisions to commit to any telescope.

Secondly, the reason refractors perform so well is that having no central obstruction at all and with good optics, they will deliver a textbook diffraction pattern with the maximum energy concentrated in the central Airy disk (making it brighter) and with comparatively less energy spread into the diffraction rings. Any scope with an obstructed light path (Newtonians, cassegrains etc) has a less intense central Airy Disk, and more light spreading into the rings. The effect is quite noticeable on a side-by-side comparison of two scopes working at the same magnification, and in particular this has a lot to do with why a smaller refractor often matches a rather larger reflector What's more it is dependent on transmitted power, which is image intensity squared, so what you think of as a relatively small obstruction has a more significant effect on the perceived intensity of the central peak than you evidently think - and also says lot about why a smaller refractor can indeed match a larger aperture reflector. There is plenty of optical theory to back this up, FWIW. For example, while an 8" SCT may provide a significantly brighter image on an extended object, most 8" SCT's cannot out-resolve a good 6" APO on double stars or the bright planets.

The only designs that will outperform refractors are the all-reflecting unobstructed designs such as the schiefspieglers, with the advantage of perfect achromatism. However they're not appropriate in this application for many reasons.

[alocky]

The main reason a refractor will show an Airy disc when a nearby reflector doesn't is because of its piddling aperture, not its magic powers of trans-physics resolution. I have yet to see a refractor (and I own a few) that gives a 'textbook ' as in Suiter's textbook star test. In fact, owing to the inherent spherical and chromatic aberration in even an 'exquisitely figured' triplet it is very hard to interpret the star test.
Likewise, one of my 4" f15 achromatic scopes will split Antares - only because the secondary star falls in the minimum between the central dot and the first airy ring.
Again, Mark is bang on the money. The average punter at a public observing night is not impressed by the concept of averted vision- my experience is that less than 5% will 'get it'. Nor will they remark on the glorious airy disc or high contrast views. After watching plenty of people go through Perth obs over the last few years, the C14 usually gives the best 'wow', and the Meade 16 a close second, usually because of the target on display.
Pity a gem can't be managed in the dome. I'm now worried about when our Lx200 gives up the ghost.
Cheers,
Andrew.

[Satchmo]

A couple of points relating to previous posts:

1) In practise ,its a complete myth that a larger scope is somehow going to show less than a smaller one in inclement seeing. A smaller scope will show superficially sharper images , but will never show more than a bigger telescope, and the larger scope will always generally show more even poor seeing.
A classic memory I have of this - an APO showing a crisp small dim image of Jupiter with some festoons at the `just visible' level. At the same time a mediochre Coulter 17.5" showed a large bright softer looking image with breathtaking level of detail in the belts due to colour perception and image scale - numerous features of all different colours because there was enough light to activate the cone cells which were completely invisible in the 7" APO and the 17.5" was operating no where near its resolution limit.

2) Central obstruction issue is way overrated. Any larger telescope with a visual optimised secondary below 20% suffers negligible effect on the Contrast Transfer Function according to Dick Suiter . Similarly spider vanes although creating a visible spike do not significantly effect planetary contrast unless exceeding 1/128 the aperture in thickness according to Suiters Star testing book. Another red herring !

My 14" Newt with 20% obstruction and standard 3 vane spider , has shown salt and pepper granulation inside certain markings at Mars opposition which I have been able to correlate with photos from the HST....

[Wavytone]

Mark, I'm quite sure it would - in good seeing. Likewise I had the chance to observe Jupiter and Saturn several times with the old Reynolds at Stromlo (a 30" f/15 Cassegrain) between photometry assignments - likewise it was staggering.

The trouble is, the seeing at observatory hill is not good and it has 3-4 magnitudes of light pollution, so to be perfectly frank any telescope there is just a MUSEUM PIECE, not something anyone will use for serous observations of anything.

I used to live at Waverton across the other side of the harbour and I tried observing from Observatory Hill, Balls Head and Berry Island several times but gave it away because the seeing was invariably poor. In 4 years I never saw what I would describe as good seeing above 6/10.

Where I am now on the ridge in Killara there is often a NE sea breeze in the evening bringing laminar flow and this makes a HUGE difference, at least good views of the planets are possible with my 7" on many nights.

As for the effect of central obstruction I'll do the maths and post some charts so you can see. I don't agree with you on that score.

[gregbradley]

Did you mean Mark? You're arguing my case here.

Greg.

[Wavytone]

I'll suggest we are in violent agreement concerning the seeing at Observatory Hill.

The problem is the choice of telescope. As I indicated before what is needed is a museum piece to impress the public, not something for serious observations of anything.

Geoff's hints confirm my own experience from living at Waverton - its going to be limited to the moon, the bright planets, bright double stars and a handful of nebulae, clusters and maybe 5 galaxies for the really interested. A couple of filters might help to but the light pollution form the harbour bridge, though I'll confess I didn't try this.

Perhaps the odd passing comet near the zenith (Halley).

Considering the French government has just passed a law requiring businesses in Paris to cut unnecessary lighting I'd suggest the observatory could do rather more to champion the cause against unecessary lighting - starting with the Harbour Bridge and the SCG. Just turn it OFF. A green initiative that no-one can argue against.

[gregbradley]

Yes.

Tak Mewlon may be a good choice as it takes in most of the points being talked about in this thread. It has a small central obstruction, its got really small spot sizes, its compact and would most likely fit on a fork mount and it regularly gets rave reviews as a visual instrument. Plus its a decent aperture.

Whether or not it would be held back by the weak seeing I suppose all scopes are in the same boat there.

Greg.

[Wavytone]

Greg, the problem isn't the OTA. Lots of choice provided the observatory can accept commercial grade stuff, and the choices haven't changed in 70 years.

The challenge is the mount and electronics - finding a solution with a life >15 years and not being dependent on a company in need of life support (Meade, Celestron) is a real problem.

The alternative is to accept "cheap and cheerful" as the amateurs do, and chuck it out every 10 years. This decision is a lifecycle cost issue and involves the long-term cost of finance available to the observatory and a whole lot of other issues unknown to anyone here.

There is merit to the concept of buy whatever cheap gear is available at the time and throw it out after 10 years, vs a telescope for the long haul. Instinctively amateurs are driven to the cheap stuff as optically it CAN perform just as well, and you have the advantage of much better observing locations with good seeing.

Most of you put optical performance as the highest priority and this is where the trouble starts - the problem here is that optical performance is almost irrelevant and takes a very third-place after cost, and aesthetics.

Ultimately the bean-counters will prevail. What is important is to present the long-term cost forecasts for each alternative for say 20, or perhaps 50 + years.

Time to revisit Decision theory - 101.

[gregbradley]

There are lots of high quality mounts these days. More now than 5 years ago.

Astrophysics, Takahashi, PME, PMX, Losmandy, ASA DDM, Planewave.

Of course these are all GEMs. But whats the advantage of an Alt Az mount?

For $10,000 at the moment you can get a PMX. It holds up to a 14 inch RCOS.

Astrophysics have the AP900 which is similar and a new AP1600.

These high end mounts should last longer than 10 years.

Greg.

[Wavytone]

All of which pose exactly the same problem the observatory has now with the 16" regarding proprietary hardware and obsolescence.

I'm rapidly coming to the view that the only way to get around it is either:

a) settle for a low-tech equatorial mount that tracks, with an RA worm drive and little else (similar to the Losmandy mounts), forget about GOTO and all the rest. The point being that if the supplier dies, there's a fair chance a simple and reliable drive train can be can be cobbled together out of parts available locally. Keep the OTA, keep most of the mount and no software involved.

b) if you adopt auto-guiding, push-to, GOTO or computer interfaces, at least adopt what is becoming an industry standard with some chance of being able to replace parts when they fail. But - here's the nub - there are no industry standard interfaces > 10 years old. That means be prepared to dispose of the whole scope after 10 years because the available technology will change radically (and incompatibly) in that time. Changing the mount almost certainly will mean a new OTA and vice-versa.

[Bassnut]

Hehe, its gone full circle to what Geoff wanted in the 1st place. A 17in CDK with Mathis fork mount (no head banging GEMs). Off the shelf, reliable, lookin good and proper just standin there, visual only, wow factor bright closeups. He just wants to have a peek though a 17in CDK before purchase.

[Peter.M]

I think all of us in here have put to much effort into what an expert would see through the scope. The bottom line is, the people looking through the thing wont know the difference. It may as well be a giant kaleidoscope to them. I suggest that what needs to be taken into consideration is not optical quality or design, but what the scope looks like.

They want a bright pink fishing lure that was designed to catch the fisherman, not the fish. From here it would all come down to preference, but I love the look of big folded scopes on equatorial forks.

[strongmanmike]

My experience is based on direct night after night side by side comparison from a light polluted commercial precinct in Canberra (The Trades Club) ie very similar to Observatory Hill (Not Wiruna) between a super high quality refractor with an equally super high quality and very expensive 16" F5 Newtonian. It is indeed very relevant to the discussion since we are talking here about potentially replacing a 16" scope, just as we had at the Canberra Observatory...aaand we essentially did replace the 16" and we replaced it with a 7" APO! simple ;) As I said and based on extensive experience at a Public Observatory equipped with the some of the best scopes available including a C14 - for a public observatory in a heavily light polluted site a 7 -10" APO on a quality well known and therefore well supported mount, would be my 100% recommendation, without question :thumbsup: and although sporting a smaller aperture and therefore dark sky abilities, to the lay person an equatorially mounted 8 or 10" refractor on a GEM will visually impress miiiiiiiles over a weird looking 20" Dob (that requires a ladder) :rolleyes: ... and in spades! :)

Takahashi or Astrophyics mounts will be supported well into the foreseeable future I am sure.

Mike

[Wavytone]

Mike, Hence my remark several posts ago about doing a site survey. I have no idea whether the observatory has done this, quantitatively. Never mind the mount, it is a separate issue.

As before this is a MUSEUM. Aesthetics and long-term lifecycle-cost count for a lot more than optical performance. Nobody in their right mind would do research at this site.

Mark - regarding the refractor vs the reflector argument the maths does support Mikes claim - and my own experience: given an APO refractor with good optics it does indeed take a reflector of 1.5X the aperture to match or do any better. Fast dobs optimised for faint fuzzies (not high power) are simply not relevant due to the light pollution. At the moment I am wrestling with Bessel functions in Excel to draw the graphs for you.

[alocky]

Dome considerations aside- the scope that everyone wants to have their picture taken next to after the sky tours at Perth obs is the 12" Calver - a 100 year old lump that still works beautifully, and has a bit of history attached to it. Sounds like the sky is so bad at Sydney that maybe something nice to look at rather than through would be the go- maybe you should try and prise that 5" Unitron away from Unipol on this forum? Now that's what a real telescope looks like!
I'm surprised by the apparent level of funding available too, given the instrument under consideration - Perth Observatory could learn a lot from Sydney Obs when it comes to securing funding!
Cheers,
Andrew.

[Wavytone]

lol... fuggedabout the Calver... This is in a category all by itself:
http://platypusart.com/wetherell/sculpture_greatwetherellrefractor.h tml

Now that's what a real telescope looks like!

[alocky]

Yep - work of art that. Wasn't he trying to sell it recently?
But the Cavler is 100 years old and played a role in confirming relativity- that's what gets the punters excited.
Cheers,
Andrew

[Satchmo]

Nick

You don't seem to have really been absorbing anything that I have written in this thread. In modern times, the F ratio of the scope is irrelevant to whether the sky is light polluted or not. With the right combination of modern eyepieces ,a fast F ratio scope is capable of the same range of exit pupils/ magnifications as a longer one - so the F ratio is irrelevant is not a consideration when we are choosing a scope for a light polluted sky. Perceived sky background field brightness is a function of magnification/ exit pupil and not of the F ratio. Do you agree with that ?

Please explain to me exactly what you mean by a ` fast dob optimised for faint fuzzies' not high power ' and maybe we can get somewhere.?

The contrast transfer function of a compound telescope is equaled by an instrument having an unobstructed aperture equal to the diameter of the scope minus the diameter of the secondary mirror so the factor in a typical visually optimised scope would be 1.2X the refractor aperture not 1.5 X...this has been written up in Sky and Telescope a few times.

[Satchmo]

The sky in Canberra would be far better than Sydney Observatory. A 6" scope of any kind would show next to nothing but the Moon and Planets.

[Kunama]

I think Peter has hit the nail on the head with this response. If I was to go to the Sydney Observatory as a total novice I would rather look through something that looks the part. I expect that most of the guests are there for the enjoyment of the history of the building and its contents and would rather look through a 9 or 10 inch refractor that looks like it came from the 1800s than the latest gizmos that are coma or chroma free. Most would probably find a bit of colour-fringing a desirable view, rather than perfect pinpoints of light.

Whilst The Great Wetherell Refractor does sport a TEC200 objective made from Unobtanium, to most Sydney Obs. tour guests, it could just as well be a 10" achro doublet, then at least the guest would see things like astronomers of old.

I would love to see this in Sydney Observatory:

[gregbradley]

I asked the question about whether or not a Mewlon 300 would be suitable.

I got this very pertinent response:

Hi Greg,

I visited Sydney Observatory in October last year with the group of Urania (Antwerp/Hove, Belgium). I own a Mewlon 300 that I acquired used some years ago. This is a splendid telescope with excellent optics and good mechanical construction, this is valid for the other Mewlon diameters as well. The 300 needs a good mount and preferably a permanent mounting (26 kg, OTA only). It reaches thermal equilibrium quite fast (you can remove the back end covers for increased ventilation, but I would not recommend that when you have visitors using the telescope as the main mirror is exposed partially when you remove the side covers). As all telescopes it will suffer from local seeing and the more so since it has a 300 mm aperture, it will suffer more than a 6 inch APO but it gathers more light as well. I don’t think you could afford a 300 or 250 mm APO if this exist at all, but a Mewlon comes very near that I think with much less expensive glass and a manageable length. See my website http://www.astronomie.be/Tranquility.Base/ (http://www.astronomie.be/Tranquility.Base/) . The Mewlon 250 would also be a good choice, lighter and less expensive than the 300!

Best regards,

Geert Vandenbulcke


Also if you are interested in a historical type telescope there is one at Windsor - Tebutts Observatory. I don't know if they are willing or not but its worth an ask. Its a big ole refractor that's brass and stuff and looks the part.

Greg.

[Wavytone]

Mark, I'm reading but I'll try to stay back on topic.

Firstly no-one makes "off-the-shelf" observatory grade telescopes under 40cm designed to last several decades, small enough to fit in the dome at the observatory. Any thing like that will have to be a custom one-off and its quite clear this will be beyond the budget.

That leaves amateur-grade equipment (up to 40cm aperture) which poses exactly the same problem they have now when it fails (which it will). Within this bracket the only off-the-shelf solutions with fork mounts are Meade/Celestron/Questar, the rest are all either dobsonian, or german equatorial on the basis of choosing any of various OTA and mount alternatives - but it will be a german equatorial.

Which brings us full circle to the initial premise of retaining the existing Meade 16" OTA and putting that on a commercial german equatorial.

Either raise the budget substantially to allow for a one-off custom telescope made to fit, or forget about the fork and live with the Meade OTA (or another OTA) on an equatorial, or go dobsonian.

None of these fit the initial needs Greg indicated, which implies the needs must change.

[Satchmo]

They may as well buy another latest model LX-200 as they are only USD $13,500 new. The driven ALT AZ configuration is as close to ideal as can get in that setting when the public are concerned. With the low balance point ,the eyepiece doesn't change height much and the eyepiece orientation is always constant, compared to use on a fork or german EQ which would require a lot of constant star diagonal rotation for convenient viewing on different objects.

Sell the old tube and mount will offset the cost, and this time buy a few of the critical circuit boards boards now, so as to increase the longevity /service length of the instrument. In 10 years time they might require narrow band filters with an image intensifier eyepiece and the raw aperture will be irrelevant.

I can't think of any more cost effective solution- the 16" is supposed to represent state of the art technology in contrast to the old refractor, putting in a second refractor would not be true to this aim.

[Wavytone]

Mark, I think this is where they will end up - another 16" or maybe that 20".

I've been waiting to see if anyone else would twig to the concept of buying "through-life spare parts" which should include at least 1 spare of each type of electronic assemblies, switch/sensor and cable assemblies, motors and any mechanical parts prone to wear such as clutches, springs and bearings, and consumable parts and materials such as cork gaskets or lubricants that may need to be replaced during a major overhaul (I'm thinking of whatever is used to mount the corrector plate, and the lubricants in the mount and focussing mechanism). This applies to not just the mount but the OTA as well.

It is not unusual to ask the supplier to provide a spare parts assessment to determine the quantities from a reliability analysis, and buy an initial set of spares followed by a larger set of spares a few years later.

Another useful technique is thermal imaging of the electronics to identify the components that are running hot, and obtain spares of these (usual this means power supply components), as they're often the first to fail. Making changes (adding heatsinks) to alleviate this is sometimes done.

There are other issues, too. If it becomes necessary to attempt repairs at the level of components on the circuit boards, it is necessary to know what components contain firmware, whether there are licences/keys in embedded software, and whether these are invalidated by conducting component level repairs. For example, with Windows XP embedded, it is not possible to obtain new licence keys and entire CPU assemblies may have to be trashed.

The observatory should make sure they acquire any special tools and documentation needed for fault diagnosis, disassembly/repair/reassembly, beyond what would normally be found in an optical/electronic workshop.

Meade should have a fair idea by now of this, at least for the 16".

An "end of life" spares purchase should be made too, prior to the cessation of the support from Meade for the scope, or the prospect of Meade ceasing to do business. In some industries suppliers will provide key customers with advance notice when it is time to make an end-of-life buy, as it helps them clean out the remaining stocks of bits & pieces when production has ended.

The experience of the previous LX200 would be fairly useful in these respects.

[strongmanmike]

Meeah...perhaps marginally better, The Canberra Observatory was in a shopping/restaurant hub of the city though, so it was pretty crapola...

In any case, as I have said a few times now (:lol:) it was my direct experience in a public setting, under heavily light polluted skies, that the 7" Starfire gave better views of pretty much everything, stars, PN's, nebula and even galaxies, compared to the 16" to the public eye at least, heck, the skies were so washed out it wasn't worth the effort to have people climbing the ladder to the Newtonian focus of the 16" almost everyone was bitterly dissapointed....the scope did look bloody amazing though :eyepop: and was a fantastic showpiece for the 7" Starfire and most visitors thought they were looking through the 16" anyway...unless I told them :lol:

Mike

[LightningNZ]

If I may add my 5 cents... I worked for 10 years (1993-2003) as a public night astronomer at Wellington's Carter Observatory and managed to rack up many hundreds of hours at the scopes there. My experience backs up both Mike's posts (and a few others) above.

There are two main telescopes housed in the domes there - a 9 inch (22.5cm) F/15 Cooke-Apo refractor (now 9.75 inch doublet) and a 16 inch (40cm) F/15 Boller & Chivens Classical Cassegrain. The long focal lengths meant even with long eyepieces we go moderate magnifications. Higher mags darken the sky background while stars look just as bright as they did before. Double stars and clusters were the main event if there were no planets or moon around. Focal ratio itself may not make a difference to the sky background but a long focal length scope will reach decent magnification with a longer focal length eyepiece, and they will generally have better eye relief, which is essential to a public observatory that will have eyeglass wearers who need to leave their glasses on.

The public all wanted to see the refractor. It was big, old and impressive looking. It looked like what the public thinks a telescope looks like. The Cassegrain was just weird to them.

The seeing is also notoriously bad in Windy Wellington, so you'd never want to push the magnification too high anyway. Only a few nights a year would the Cassegrain outperform the refractor. The diffraction meant stars were never quite as punchy in the Cas as they were in the refractor either.

My opinion: Get an apo refractor of moderate size and focal length, so it's not too hard to get your eye to. Also get a couple of smaller scopes of differing focal lengths, and two reasonable cameras and have a wide-field and a close up of whatever you're viewing on some TV screens nearby. If people can't look through the main scope, at least they see something. Even they do get to look through it they have something to see while waiting in line. Also: Don't worry about the mount being a German Equatorial - just use a short counterweight bar and some very heavy weights. Have the thing up on a pier, you'll be fine. You can always put glow-in-the-dark star stickers on the counterweight assembly.

Best wishes to the Sydney observatory,
Cam

[gregbradley]

Maybe something like this:

http://www.astromart.com/classifieds/details.asp?classified_id=810026

Greg.

[Satchmo]

Mike - You seem to be completely mis-informed about the quality of Sydney skies here. Canberra skies would be way way darker than Sydney CBD in the heart of a population of 5 million- you are lucky to see more than a few brighter stars by naked eye. When was the last time you stood on Observatory Hill and looked up at the sky? I contend that a 6" telescope would be completely useless there.

[Varangian]

I think you're being a tad unfair. I think you need to understand that many people new to the observatory may just as easily walk away from the eyepiece not having seen anything anyway and be equally disappointed. At least something, even if on a screen, may give them the hunger to follow up on the possibilities of observig what's out there, whereas a few blurry glows really doesn't incite much curiousity to the uninitiated.

It is always first preference to observe through the eyepiece, but so people won't be disappointed during their visit maybe Alex's set up is a viable alternative.

[Barrykgerdes]

Fred is correct.

I don't think many of the people making suggestions have ever been to the observatory. One of the advertised features is to look through the big telescope at the sky.

Twenty people in the dome does not give much space for moving around.
That is the advantage of the small footprint of a 16" SCT on a fork mount that allows ease of access to the eyepiece for most people and a 16" SCT in a confined space still looks to be gigantic.

Barry

[alocky]

I understand they've already got an old and extremely credible looking large achromat in one of the two domes, so that's already covered. Re-reading the original post it seems that there is also nothing wrong with the 16" at the moment, other than it does not cut it in the Sydney light pollution. Although the original poster has probably long lost interest as this thread roared off at a tangent, it seems that what they need is better expectation management, and perhaps a good light pollution filter.
I doubt that increasing aperture by a few inches will produce the step-change in the visual experience of a casual visitor they are looking for.
I sometimes wonder if having the corridors and museum at the Perth Observatory lined with large and colourful astrophotos is setting up the visitors for dissapointment. Certainly these days, someone used to seeing the kind of images common in the media is underwhelmed by their first look through a telescope. Unless it's of Saturn.
cheers,
Andrew.

[Wavytone]

+1.

And even fewer have tried to use their own scopes either at observatory hill or nearby, for a specific astronomical event, with sufficient time to "appreciate" the conditions that prevail.

[Satchmo]

Ok this makes 102 posts. I suggest we form a sub-commitee to decide how we might get them all printed out and bound , and present to Sydney Observatory as a think tank, and then they can form a sub- committee to examine our findings and report back here for further comment :)

[LightningNZ]

Last time I went to Sydney Obs was back in 1995. Haven't really had an opportunity to go back there. I somehow doubt the experience I get going to a public observatory is really the same as that of a regular member of the public going through the same place. ;)

That said, there are several people here have spent quite some time working in public observatories and we tend to be saying the same things.

Cheers,
Cam

[Wavytone]

Haha I'm sure Geoff is keeping an eye on this thread. And I think it isn't making any more progress. Committee ? Thanks but I'll pass on that.

[ausastronomer]

Well you're right. I haven't been near the place in about 15 years. But why would I want to, I have high quality visual scopes to 30" aperture under my thumb, under mag 7 skies. I have an 18" Obsession in my shed, located 4.6 metres from my Delonghi coffee machine with Mag 6.2/6.3 skies on my back porch.

What you need to appreciate is that you have had a lot of contributions from some very experienced visual observers, some of whom have worked in public observatories, and many like me who have done a lot of public outreach, over many years, under all types of sky conditions.

Whether a medium aperture APO (6"/10"), or a medium/large aperture SCT, or a medium aperture Mak or Classical Cass is the right solution is open for debate. What everyone almost to a man is tellin you is that to buy a 17" to 20" Planewave would be pissen an enormous amount of taxpayer provided funding against the wall, for nought.

Something else to consider is what has seriously been done to see if the electronics in the mount can be rebuilt, outside of Meade.

Has anyone bothered to ask Gary if the mount is salvageable and at what cost? He is as knowledgeable as anyone on the planet in regards to mounts and mount electronics. (http://www.wildcard-innovations.com.au/) It may be cost prohibitive and he may not have the time, desire or inclination, but it will not cost the earth to at least ask the question and it may be something he would take on with a sense of pride and self satisfaction involved, knowing the cause it was for.

[mithrandir]

I can't see the problem with getting a commodity 14" or 16" fork mounted SCT and accepting that the mount will not last forever. The amortised price would undoubtably beat any solution using something really designed for photography.

The OTA may well be saleable when the mount has to go. When that happens they'll get better electronics with whatever they buy to replace it. As long as they keep spares on hand, the time to upgrade is when the spares run short - not when they run out.

From the few outreach nights I've been to - with better skies than you'll ever get in the CBD - what customers want is to look through an eyepiece attached to some largish scope. Something on a screen keeps them interested while they wait, but that is not why they came and paid their money.

[clive milne]

Hi Geoff,

If I could offer a solution that meets all your functional requirements (if not in the exact terms you stipulated):

Please consider a derivative of the German equatorial design with an extended polar axis such as the ASA Direct Drive DDM160
http://www.astrosysteme.at/eng/mount_ddm160.html
To avoid duty of care issues associated with counterweights, simply orient the telescope such that it operates past the meridian with the counterweights high in the air, like so:
http://www.apm-telescopes.de/media/images/secondhand/popup/2042/APM%20Apo%20Bino%2012%20inch-22.jpg

This is a turnkey approach with a proven track record boasting professional level reliability that will work with your existing 16" OTA and is easily upgradable to a much larger instrument if and when required.

If you wanted to save money, you could basically achieve the same thing using a generic German equatorial head with a custom pier that gave the same clearance for the OTA. A slightly modified AP1200 would be quite a bit cheaper but do everything you required without the public safety issues normally associated with counterweights. (you can pick them up for under $10k landed in Aus if you're smart about it)

regards,
~c

PS: Ice in space might not be the best place to solicit advice on such matters.

[gregbradley]

Probably more important than which scope is which light pollution filter or which narrowband filters.

A nice Ha and Hutech light pollution filter may do wonders.

Greg.

[clive milne]

Greg... you do mean Oiii, don't you?

[gregbradley]

As you can see I don't do a lot of visual. Yes O111 would be good. A wideband Ha would work though wouldn't it?

Greg.

[clive milne]

As a discrete band, not at all.
The photoreceptors in the human eye responsible for our night vision (rods) are completely blind at the wavelength of H alpha - 656nm.

~c

[GOTO]

Hi all,

Here is an image of the north dome scope as requested. Again, let me state for the record we take our fiduciary duty very seriously and will not, nor have we ever, wasted taxpayers’ money.

We would still like to look though a Planewave if possible but we understand the comments made here.

I can’t answer all the points that have been raised but a few comments in no particular order:

1. We are a museum and our needs are different to most people here on IIS. We are very much aware of the terrible seeing in the CBD.
2. Nasmyths look like they are out of our budget ☹
3. Newtonians are out, as we won’t send people up high ladders.
4. Refractors are out too. We have one that is 290mm (1874 Schroeder) and the height for viewing positions varies too much.
5. Video will only ever be a secondary experience.
6. We are following a few ideas that have led us to Germany.
7. We haven’t given up on the option of re-mounting the 16inch OTA in which case video supplement would be desirable but can never replace the eye at the scope.
8. We won’t consider a 20inch Meade until we have seen others use one first and reviewed it extensively. Do they actually exist yet? Besides it is a GEM.

Clearly there is no easy solution.

Kind regards
Geoff

http://i39.photobucket.com/albums/e185/Tokyo1989/NorthdomeGeoffo-small_zpsbf39a1ad.jpg

[Satchmo]

John: I'm sure someone could do a retrofit of Servocat or Siderial technology unit given a few dollars.

As I said before the small footprint of that 16" in ALTAZ mode and the fact that the eypiece changes only a little in height make it still a very good solution. i wonder whether an image intensifier eyepiece like the I3 in front of a light pollution filter give the scope more legs.

[Barrykgerdes]

That looks just like I remember it when I first saw it in 1997. If the electronics in the LX200 are still OK they will probably last forever. Fitting a servocat would be more trouble than its worth. I certainly wouldn't attempt it under $5000. The 20" Meade is not realy an option on it's GEM. I think Don at Bintel and I can keep that LX200 going a little longer as long as you don't have a major failure.

For the use you require the modern LX200 GPS would give you a little more ease in setting up because of the GPS and auto align and the fact that the Autostar 11 is almost identical to drive as the old handbox. Other than that. "If it ain't broke why mess with it"

Barry

[GOTO]

Hi Barry,
The GPS doesn't work because the scope is in a metal dome. We did try an antenna out the dome but that didn't work sadly so we do a blind two star alignment each morning.

The electronics are playing up. Every now and then the scope just drives off by itself, typically toward zenith but not always.

If I remember correctly (as we've been swapping scopes around so much) we reversed the main dec/altitude gear as it was badly worn.

Not complaining though as the scope is used day and night every day bar two per year.

Cheers
Geoff

[Barrykgerdes]

OK Geoff

I got the impression that it was still working. The problem with taking off every now and then is difficult. It happens with the smaller LX200's occasionally. I have never been able to trace exactly the cause because it has always come good when I get to testing the boards. I think it is a problem with the sensor arrangement and adjustments on the motor boards when the components age.

If the dec gear is worn that badly with the use you give the scope it sure looks like you need a replacement scope. I think the 16"LX200 GPS is the best option at the momnent but it will need to be setup without thd GPS. That means setting the date time manually. This can probably done easiest from a computer. This still may avoid daily alignment if the scope is parked each night after use.

I no longer have my 12" LX200GPS so I can't easily test a way of getting the date/time without the GPS. With the GPS working I only aligned the scope once and then parked it so it held its alignment for 5 years.

If you do end up getting another LX200 I would be happy to help with settiing it up.

Barry

PS I don't see the poor seeing conditions at the observatory as a major drawback in the use the scope will be put to. As has been said before the patrons only want to look through the eyepiece of a big telescope and most of them will only be interested in the moon and planets.

[Wavytone]

Geoff,

There are several ways to accurately focus a scope for infinity, which I'll post here as I am sure others may be interested. My own experience with public nights indicates quite a few people are a bit short/long sighted but have been ignoring it - when they try to look through a scope their focus is significantly off, and as a result they need to refocus a telescope to see anything properly.

Of these:

- I often use method 1 and method 3.
- Method 1 is not so accurate,
- Method 2 assumes your eyepieces are parfocal;
- Method 3 is quite accurate, and does not rely on your eyepieces being par-focal;
- Method 4 works in daylight only;
- Method 5 is obvious to camera buffs, and requires a specially modified eyepiece;
- Method 6 works for a point source (stars) only and requires a specially modified eyepiece;
- Method 7... requires a camera and makes some assumptions about your eyepieces. I have used this a few times but is fiddly.

1. The first method is simple - put your glasses on and focus while wearing them ! This relies on the simple fact that over 45 people lose their ability to accommodate different focal distances (I'm 56) and if you have some glasses that have been accurately selected for long-distance by a good optician (as mine are), then your eyes should have perfect focus for infinity when wearing them. I have separate reading glasses. It's even a good reason to go see your optician regularly when you are a bit older :)

If your glasses are chosen for a range of 1-2 metres (rather than infinity) this may not be a bad thing either, as most can manage to focus on that.

2. If you have parfocal eyepieces (mine are, Vixen LVW's) switch to the shortest focal length eyepiece and focus with that (on anything) then leave the focus alone and switch back to whatever eyepiece you wish. For low power eyepieces this will give an accurate focus - if the eyepieces are parfocal.

3. The next method works for small objects with a well-defined edge, particularly the brighter planets (Venus/Mars/Jupiter/Saturn). Having got the object reasonably well centred and more-or-less focussed, slowly pull your head back a few cm from the eyepiece while continuing to look at the object.

If it stays in focus - and it's apparent diameter STAYS THE SAME (the latter is the most important part) the 'scope is focussed. If it's apparent diameter increases/decreases, the eyepiece is not accurately focussed. This method is incredibly sensitive at high magnifications on the planets or moon, and very accurate.

4. This is a variation on 3, easy to do in daylight as you need to be able to see the exit pupil of the light cone coming out of the eyepiece. Point the telescope at blue sky so you can see the blue disk of light (the exit pupil) emerging from the eyepiece. Using a dynameter (a tapering slit with a numbered scale), hold the dynameter at the eyelens and measure the apparent width of the exit pupil at the eye lens. Now pull the dynameter back away from the eyepiece a few cm and measure the apparent width again. Should be the same diameter if focussed. If not, adjust the focus so that it is the same width.

This is easy to do in daylight. if you are tempted to set it then wait till dark, remember your telescope OTA may shrink as it cools and the focus will shift.

5. The next also assumes you have parfocal eyepieces, and one of them has a piece of ground glass in its focal plane. The ground side must be facing the telescope. Put this eyepiece in the scope and focus on anything bright - moon, planets or bright stars. I was able to cannibalise an old eyepiece which had a filter thread cut well into the barrel, and an old filter which I ground with some spare abrasive (wet-and-dry carbide paper, grade 1600 will do this nicely). There are 2 tricks with this one

a) to set up the eyepiece with the ground glass accurately in the focal plane of the eyepiece;
b) to add a ring around the eyepiece so it is parfocal with your other eyepieces.

To do these accurately I used an optical bench.

Alternatively, if you pick up an old film SLR body and dismantle it, you can cannibalise the focussing screen. Many old SLR's had a central split-focus or micro-prism surface that provides a much brighter image than ground glass, notably any of the Pentax MX, ME or K series bodies which had a plastic screen easily reworked to fit an eyepiece with a Dremel and some sandpaper. Put masking tape over both surfaces to prevent scratches while you're working on it.

6. Basically this method is a star-test and it is VERY accurate but also quite fiddly and time-consuming. You need a 12mm eyepiece modified so that:

a) it has a knife-edge, graticle or very fine wire in the barrel, but this must be somewhat out-of-focus in the eyepiece, ie located in front or behind the field-stop by a couple of mm.

b) You need a collar fitted so that once the knife-edge or graticle is at the focus of the telescope, your other eyepieces will be par-focal with the knife-edge (and not par focal with the lenses in this eyepiece).

You will need an optical bench of some sort to make this modified eyepiece.

With a star in the field of the telescope, look into the eyepiece, it should be a out-of-focus so you can see a disk of light instead of a point. Allowing the star to drift across so the knife-edge or graticle cuts into the light-cone near the focus, you will see the disk go dim then blank. If it goes dim evenly all over, the knife edge is precisely at the focus. if it goes dim on one side first, the knife edge is in front or behind the focus, so re-focus and try again. This takes a bit of practice to get used to.

Way back in the 1970's I used this method to set the focus for a cold-camera plug on an 8" Newtonian. It is incredibly sensitive, and you are seeing a Schlieren view of your objective which will reveal any tube-currents and atmospheric turbulence. This may be so bad that you can't accurately focus.

7. This last method works especially well at high magnification. It relies on eyepiece projection into a good quality compact camera with manual focus (i have a Panasonic LX5), you can use this on the moon or bright planets but its impossible on anything else. To work well, the eyepieces should have enough eye relief to put the exit pupil at the iris inside the camera lens so that it will fill the field of view of the camera without vignetting (again, I'm using Vixen LV and LVW's that have a pretty consistent 20mm ER.)

Basically, I manually set the camera aperture to f/2 (iris wide open), choose a rough ISO setting (ISO 100 for the moon, or 1600 for Mars/Jupiter/Saturn) and manually set the camera lens focus for infinity.

Holding the camera at the eyepiece, focus the image in the camera using the telescope focusser (the camera's autofocus must be disabled). Once focussed, remove the camera.

In my case the rubber eyecups of the Vixen LV and LVW eyepieces are a neat fit and will hold the LX5 in place without rings.

[ericwbenson]

Hi Geoff,
From reading your criteria and comments:
You seem to like the OTA - it provides pleasing views for the public.
The mount is unreliable and must be replaced.

I think the solution is simple...one you have already considered, replace the mount with another fork mount. In this size of telescope the only fork mount to consider is the Mathis MI-500 (MI750 if you think you might upgrade the OTA one day). Yes they are expensive but you get what you pay for and this mount will probably outlast the dome. I am sure Mathis Instruments have made adapter plates for the 16"LX200, it is certainly waaaay within their capability. Otherwise you could get rings from Parallax Instruments to mount to plates which attach to the fork. I bought rings for my C14 and it was no trouble for them to tap both flat mounting sides.

I have a CDK20, unfortunately for you it is 700km from me, and an even longer journey from Sydney. Before moving it into the outback I used it quite a bit from my backyard (~10km from Adelaide CBD). The views thru the eyepiece were excellent. The central obstruction is only a bit larger than a C14 (my previous scope) so diffraction is not a big worry and the correction off axis is far superior, but would a novice notice, not likely. The cost is about 10x what a C14 goes for, is the view 10x better? Certainly not thru an eyepiece (for a camera it's a different story). Seeing did limit high magnification views, but the light grasp for star clusters (which show up ok in the city) is always welcome. Galaxies, except for perhaps two or three, are a write off, but emission and planetary nebula with an OIII filter still makes use of all that aperture, little peashooter refractors ;) can't get close here.

So spend the money on the mount (familiar refrain?), a reliable mount able to point at "invisible in the finder" objects, when people are queued behind you, and then keep it there when somebody slams an elbow or noggin, is the most valuable asset to your program.

As an aside, long ago I worked at a museum too, so I know your criteria. We had to manually find objects in a 15" f/15 refractor (fl 5.7m!!!), and do it quickly, especially in winter since on clear nights it usually dropped below -15C in Ottawa. The mount was a "push to" with a clutch and clock drive, and had settings circles about 4m off the ground (that was a big pier!). You had to know how to star hop and use coordinate offsetting to find anything veiled in the sky glow, how we got by without "goto" will be legend in another generation...

EB

[Chris_Erickson]

Just FWIW on an old thread, all of the electronics for the LX200GPS-16 are still available from Meade. I own a LX200GPS-16 and work on a number of others for the Onizuka VIS on Mauna Kea, Windward Community College on Oahu and others. The mounts are solid (I didn't say precise) and the electronics are easy to repair. And a retrofit with Sidereal Technologies or Software Bisque TCS are common. And in 20 years there will certainly be other drive retrofit systems available to upgrade again, when the time comes. There is a lot of space in the big, hollow fork mount for future changes and modifications.

An important upgrade to the Meade worm drives would be to replace the existing lubrication with a 3:1 blend of Lubriplate 105 and Nye Fluorocarbon 868H damping grease. That will reduce friction, wear and noise. This is very similar to the formula currently used by a number of premium mount makers.

The advantage of Alt-Az over polar is that the eyepiece doesn't move around a lot and is more convenient for access by the general public. The Onizuka VIS uses adjustable-friction, rotating 2" SCT thread adapters that allow a standard 2" diagonal to be easily-rotated to different angles for different viewers. They are made by Starizona. I machined a 4" to 3" SCT thread adapter for them so they could use the 3" C14 adapter on their 4" port on their 16.

I would also suggest getting some newer, wide field eyepieces and get rid of the junk eyepieces I looked through on my visit in November. Broken, trash eyepieces give trash views. What an embarrassment.

And it would be nice if someone were to invest in getting the mechanical drive system repaired on the Schroeder refractor. It likely only needs to have its mechanism cleaned and relubricated but apparently it ground to a halt about ten years ago and still isn't fixed? What a shame. There are probably at least ten camera repairmen in Sydney that would be perfectly-capable of repairing that clock mechanism. Another option would be to put a simple gearhead servo motor and microcontroller directly on the RA worm gear and bypass the old clock mechanism. That could be done with minimal modification to the mount and would likely be fully-reversible in the future, if desired.

It would also be nice if the docents had a proper foundation in astronomy. For example, have them stop telling the public that meteors burn up because of friction. It is the rapid compression of gas in front of the object. PV=nRT.

I am a consulting observatory engineer that works for the observatories on Mauna Kea and others around the world. The Sydney Observatory is an incredible, historic observatory that with a few fixes and improvements, could be doing fantastic outreach. Unfortunately that doesn't seem to be happening right now. :(