The perfect scope … advice required!

[Satchmo]

I wasn't so much suggesting that *some kind of astrophotograpghy* can't be done with an big dob. Okiskopey I'm sure has his I eye on emulating the kind of deep exposures the astrophotographers are doing generally with german equatorial mounts, not just stacking 30 sec exposures.

Again, the question here was about astrophotography with a ServoCat. I know 700 have been sold , I know they are great for visual or CCD planatary stacking, but I've never seen a single serious long exposure picture with a big dob taken through one, thats just a fact. Please post links if you find any.

This thread started because Okyscopey wants advice on how to distribute his retirement funds to do all the astronomaical things he wants. Clearly , and as you achnowledge, alt-az photography is at the cutting edge for bold tinkerers, and to my knowledge it is not being done with Servo Cat systems, otherwise such examples would be plentiful by now. Okiscopey does not necessarily want to embark down tinkering endlessly at the cutting edge . He was looking for sound advice on what is doable now?

On the subject of planatery photograghy, large dobs are generally not so suitable as medium aperture all metal scopes because of thermal issues. The worlds best planetary shots are being taken with 40% obstruction C14's and good seeing which shows how important cooling is rather than aperture.

Originally Posted by rumples riot

Sorry to offend, but I have been around for a long time and heard lots of people say things that can't be done or you are using the wrong scope for that. Positions of ignorance suggest more research needs to be done, by those making the statements.

Mate, you've not offended me, I've been around optics and telescopes for 35 years and I think I've got a fair idea of whats going on. I've 'researched' the idea of DeepSky photograpghy with a Servo Cat and as I've said I can't find any serious results.
Cheers, Mark

[xelasnave]

Get the Meade max... you know you want one. I know I want one but dont want to sell a house to finance one...
If you want perfect have a look at this...

http://www.rcopticalsystems.com/24inch.html

AND...Stacking for dso's will blow you away.

I was on the same line of thinking until I realised that photos will show so much.

I have a 12inch for visual but use only a 6 inch reflector (SN) for photos and the results from stacks of 200 second runs produce I would expect better than anything visually thru even a very large scope.

I really think the most important thing is the darkness of the site and having a pier, a good eq mount, time to get perfect polar align and something to house everything.

If thinking photos concentrate on the mount.. have a look at what an good 80mm can produce on a Paramount Mount for example...

best wishes
alex

[ausastronomer (John Bambury)]

Originally Posted by MortonH

Hi Mike, this decision is one that we all dream about!

What about using the 24" SDM for visual only and having a smaller, equatorially mounted scope for imaging? I'm not sure what the servo cat, etc. costs so I don't know what kind of scope you could get for the money saved by not driving the SDM (you could still have Argo Navis for finding stuff).

Whatever you decide, please invite me for the weekend!

Morton

Having an 18" Obsession fitted with Servocat, I can say "I" will never own another dob without servocat fitted to it. It adds at least another 10% to 15% to the aperture of the scope by having the object stay perfectly centred while you are studying it.

Deleting the Servocat (or the Argo) is not an option IMO, on such a premium piece of equipment. Buying a small refractor for imaging is the right option IMO, but do not butcher the main scope for the sake of the toy scope.

Cheers,
John B

[ausastronomer (John Bambury)]

Originally Posted by rumples riot

Sorry to offend, but I have been around for a long time and heard lots of people say things that can't be done or you are using the wrong scope for that.

Paul

Hmm,

That's obvious on the basis you bought a beautiful timber truss dob with a 2" thick mirror for planetary imaging and then had to hack holes in the box because of cooling issues.

Personally, I would have ordered the scope with a 1.6" thick mirror from Mark or Carl Zambuto (both are offered as mirror suppliers), if I wanted the scope for planetary imaging. This would have resolved most of your cooling problems. I can tell you from experience that my 2" thick 18"/F4.5 OMI mirror, while superb, takes forever to cool with 4 fans on it.

You may have been around a long time, but you didn't learn much about mirror cooling and large aperture telescopes

Cheers
John B

[Satchmo]

Just adding to Johns point here, I'm not casting any aspersions on ServoCats, just to be realistic of what they are capable of. They do what they were designed to do ( visual tracking), brilliantly. I'll have one on my next `big' bino for sure.

Mark

Originally Posted by ausastronomer

Having an 18" Obsession fitted with Servocat, I can say "I" will never own another dob without servocat fitted to it. It adds at least another 10% to 15% to the aperture of the scope by having the object stay perfectly centred while you are studying it.

Deleting the Servocat (or the Argo) is not an option IMO, on such a premium piece of equipment. Buying a small refractor for imaging is the right option IMO, but do not butcher the main scope for the sake of the toy scope.

Cheers,
John B

[xelasnave]

I really like this one...
http://www.mistisoftware.com/astrono...pment_RC32.htm
alex

[okiscopey (Mike)]

Now this is getting interesting!

From the first lot of replies I gathered that in a fixed set-up, a big SDM (or equivalent) couldn’t be made to ‘do everything’ when fully optioned-up, despite the optical quality, the aperture and the focal length.

The standard answers suggested it’s best to stick to the usual different-equipment-for-different-jobs scenario - and I may well go down that track.

I thought the thread was dormant, now I find it’s been revived with an interesting - err, debate - on the original question.

I’ve no idea how it’s all going to work out, but I do thank Paul, Mark et al. for the new discussion and hope others are learning as much as I am from the experts. I’d certainly overlooked the ‘thermal’ factor, and probably a few other practical issues as well.

By the way, like most of us here, I've looked at (drooled over?) the RCOS stuff ... but I’m not going to be that rich!

[sejanus (Gavin)]

I think that rather than try to make 1 scope do everything, get a big SDM for visual use but maybe instead of a 24" get a 18 or 20.

With the leftover funds get a GEM and a refractor for planet astro work.

[rumples riot]

Originally Posted by ausastronomer

Hmm,

That's obvious on the basis you bought a beautiful timber truss dob with a 2" thick mirror for planetary imaging and then had to hack holes in the box because of cooling issues.

Personally, I would have ordered the scope with a 1.6" thick mirror from Mark or Carl Zambuto (both are offered as mirror suppliers), if I wanted the scope for planetary imaging. This would have resolved most of your cooling problems. I can tell you from experience that my 2" thick 18"/F4.5 OMI mirror, while superb, takes forever to cool with 4 fans on it.

You may have been around a long time, but you didn't learn much about mirror cooling and large aperture telescopes

Cheers
John B

Actually this is totally wrong. First I have not cut holes in my SDM. I run a peltier cooling system which sits on top of the mirror box and cools the mirror in 1.5-2 hours. You are clearly wrong here. I suggest you read my blog on the investigation into cooling my SDM. This can also be verified by Bird and Dave who both own peltier cooled systems and have seen my SDM working in this manner. Patronising me when you are wrong will not convince me otherwise.


Mark as a C14 owner and someone who does hi res imaging, not all the great imagers are producing images from SCT's. Birds images this year are from a newtonian. Hi latest sets of images are clearly on par with Damians images. No one else is producing images of this quality. Large newts can be used for imaging, both DSO and Planetary with both GEM and Servo Cat systems.

Other notable imagers are Wes Higgins, he uses a starmaster 18 for both planetary and lunar.

Here is Two of many links.

http://home.houston.rr.com/gschaeffe.../astropix.html
http://www.obsessiontelescopes.com/imaging/index.html

[davidpretorius]

Originally Posted by rumples riot

I run a peltier cooling system which sits on top of the mirror box and cools the mirror in 1.5-2 hours.

yup, not mods to the body at all, the scope too good a beautiful piece of equipment to be "hacked" so to speak!

I say the jury is still out......Damian with his non actively cooled c14, but with a lot of experience and knowledge and Bird and fully automated Newt, whose inside knowledge of the way in which processing is done is second to none.

I would not like to call, whether an actively cooled 18" sdm will give better results that an actively cooled c14 on high magnification images.

The only way is to throw the scopes in a row, fly Damian P down and let them slug it out (so to speak).

It seems to me that there have been some huge leaps thanks to aussie amateurs that have brought the newts back to the c14's etc in planetary.

At the end of the day, will a "cheaper" 18" mirror set up as a newt be better than a 18" sct (if such a beasty exists).

I know my own eyes saw the quickness of setting up, aligning, accurary, high mag tracking and superb eye ball views of an actively cooled 18" sdm mirror.......great all rounder for mine! as for DSO's, well, would like to see that in the flesh one day

[Satchmo]

Originally Posted by rumples riot

Mark as a C14 owner and someone who does hi res imaging, not all the great imagers are producing images from SCT's. Birds images this year are from a newtonian. Hi latest sets of images are clearly on par with Damians images. No one else is producing images of this quality.

Yep I know about Bird's efforts, in fact I even know the guy who made his optics ;-). To be fair, Bird uses a fast cooling conical mirror and active cooling system your not going to find on a traditional large dob which is the instrument in the subject of this thread.

//Other notable imagers are Wes Higgins, he uses a starmaster 18 for both for
//both planetary and lunar.

Wes uses a fast cooling 1.6" mirror not common on traditional large dobs which allows him to hold his own with the smaller instruments.

///Large newts can be used for imaging, both DSO and Planetary with both GEM
///and Servo Cat systems.

( Stuff deleted here as I'm just repeating myself )

If the 18" dob was the best for planary imaging why then buy a C14?

. Choose the right tool for the particular job I reckon. Earlier in this thread I posted my own wish list for instumentation if money were no object, you may be interested in that as it reflects that mantra.

Cheers, Mark

[rumples riot]

Originally Posted by Satchmo

Yep I know about Bird's efforts, in fact I even know the guy who made his optics ;-). To be fair, Bird uses a fast cooling conical mirror and active cooling system your not going to find on a traditional large dob which is the instrument in the subject of this thread.

//Other notable imagers are Wes Higgins, he uses a starmaster 18 for both for
//both planetary and lunar.

Wes uses a fast cooling 1.6" mirror not common on traditional large dobs which allows him to hold his own with the smaller instruments.

If the 18" dob was the best for planary imaging why then buy a C14?

. Choose the right tool for the particular job I reckon. Earlier in this thread I posted my own wish list for instumentation if money were no object, you may be interested in that as it reflects that mantra.

Cheers, Mark

The active cooling system is not standard but it is easy to make Mark. Take a look in my SDM blog. It was dead simple and makes a large scope more adaptable to differing conditions. This is my whole point. You don't need to always abide by old conventions when things are changing. The hard work of the R&D has been done. The larger the aperture the more peltiers you need, that is all there is too it.

I know Wes quite well and you might be surprised to hear that he sits an airconditioner behind his mirror for several hours to get it cold enough. He is most interested in my cooling system and has asked lots of questions relating to it. I hope that he uses the idea. It will make his images even more brilliant.

The reason why I bought the C14 is that I own a unit. The only place to leave the SDM and image with it is out the front which is not secure. I have a pier and and deck out the back which houses the C14. It was the largest and most compact scope I could get into the space. I could not swing the SDM in that space. Also the SDM is undergoing balance tests with all the weight I have on the side. I want to perfect the guiding of the scope. It has nothing to do with using the right tools. I am a firm believer that you can do almost anything you want with large aperture. You just have to ignore the critics and use current technology. Birds idea of peltiers works on large aperture, I don't understand why you guys cannot see that.

Incidently my C14 is peltier cooled too. The very first of its kind and it works a treat. If you go to CN there is a thread on it in the solar system imaging section. Follow the links.

So that is my advice to Mike. It is not ill conceived, you just need to plan a little more and work out methods around certain issues. One large scope can fit the bill. Ultimately the choice is yours mate, but I have tried to save you spending a whole lot of cash. Try not to follow the nah sayers. The technology now exists to use a dob for both types of imaging and get great results.

[Satchmo]

Originally Posted by rumples riot

Try not to follow the nah sayers. The technology now exists to use a dob for both types of imaging and get great results.

Oh, boy I'm dipping out of this thread , the signal to noise ratio has become way too high.

[Rodstar (Rod)]

I think this is the point where Nan offers everyone another cup of tea.

[Satchmo]

Someone pass the sugar please ?

[rumples riot]

Is that the standard response here? To say your opting out and saying my comments are noise related?

Imagesplus has the facility to derotate images taken with a derotator. You can buy derotators from a number of different sources (at affordable prices) and use this to gain perfectly acceptable images. With practice fine work can be done. Afterall, large observatories have been doing this for some time now.

Incidently I have been involved in astronomy as long as you Mark. I have a different opinion to yours and unlike you I don't see a reason why Mike cannot use an SDM to good DSO imaging. Simply calling me names without supplying evidence to your argument will not make you right. Or have I got this wrong; just because you say so makes it right??????

[okiscopey (Mike)]

Originally Posted by Satchmo

Someone pass the sugar please ?

... and a couple of aspirins.

[jase (Jason)]

Originally Posted by rumples riot

You can buy derotators from a number of different sources (at affordable prices) and use this to gain perfectly acceptable images. With practice fine work can be done. Afterall, large observatories have been doing this for some time now.

I'm going to chime in here. I don't know if you've ever use a field de-rotator. They sound attractive, but from my experience the amateur versions are not accurate enough at anything over 1200mm focal length. I used the Meade #1220 for approx 6 months before selling it for half the price I bought it for (had no takers). It was a complete waste of time. If you're carrying a reasonable payload, you also need to watch out for flexure. I have not had the pleasure of using the Pyxis 2" or 3" camera rotator. These are commonly used for remote operation of object compositing/framing, but can also be configured to de-rotate fields. These are considerably different beasts to those used by large professional observatories such as this - http://www.ee.nmt.edu/~teare/fielddr.htm. You could certainly buy one of these professional units, but for the price of two 20" SDM scopes and then some.

Alternatively, you could image using CCD drift scanning techniques, but this is sub optimal for small FOVs. The level of nebulosity collected is based on the time it takes for the object to drift across the CCD registers and is read out. Thus, obtaining those faint wisps or globs become difficult as exposure time is constant.

I'm all ears to see where this debate is going. The cost per inch of aperture with large newts/dobs (14" and up) is appealing. Great visual instruments and for planetary images. However, until we start talking large dobs/newts on GEMs or Eq. fork mounts, I'm going to tune out. We all know that there is no substitute to long exposures when it comes to DSO imaging. To date, long exposures for DSOs are only practical through the use a GEMs or Eq. fork mount. I'm not convinced that a Eq dob platform (i.e a wedge) provides sufficient tracking accuracy (especially at the focal lengths discussed here).

So to this end, the "ultimate" scope does not exist. We all wish it did and some may come close. The old "horses for courses" statement applies. A superb visual instrument doesn't always apply itself well for photographic work (and vice-versa). You need to make an informed decision as to what features/aspects are important to you - there will be compromises. I guess if there is such a thing as the "ultimate" scope, it would be one that offers you the most pleasure and assists you in achieving your astronomy goals - whatever that maybe.

[Bassnut (Fred)]

Ive been fortunate enough to experience DSO imaging with the cheapest to the best equipment. As Jase said, in the end, theres no substitute for long exposures, and to that end, the rules are well defined. Going "different" is appealing, but theres good reasons why most dont, unless your a tweaking genius (granted, theres a few) it doesnt work.

Long FL DSO imaging is all mount, mount, mount. The appropriate mount required for long exposures on a long FL, large aparture DOB would be a crippling financial experience ;-).

SCTs and RCs are used for long exposure imaging partly for the reduced load they present to the mount over a DOB/newt.

Ive been amazed over my equipment owning experience, just how important the mount is (rather than aperture). Thats where the money should be spent, a good mount and then an OTA to suit.

[rmcpb (Rob)]

This thread has shown what is possible by some who put in the yards BUT for someone who wants to observe and take some good shots another option exists. Neither is "right", without the people who push the envelope we will never progress, just think about Dobson and his telescope we would not have the large apertures today. But for some the proven ease of the GEM and a smaller scope for imaging is what they need.

Everyone should just take a deep breath and have a cuppa, noone is wrong, we just think differently