Takahashi FS152 VS. Starmaster 14.5″ Hybrid [Archive]

gregbradley

21-07-2010, 03:07 PM

I owned an FS152 for years, it was my first expensive astro purchase.

It gave even to this day some of the finest visual views I have seen.

Fluorite doublet is a good formula for visual if not for imaging.

It would cooldown in no time and I was blown away by the initial views when I first got it. They were way brighter than I expected.

I haven't looked through a lot of Dobs but the guys point makes sense to me. Compound scopes are vulnerable to tube currents (micro seeing environment) that affect their ability. I had a long discussion with Anthony Wesley about this at Parkes and he has the same view on this. He of course is at the very top of his profession so his views are valuable.

6 inch refractors are also renowned for cutting through the seeing. Mike Sidonio and Marcus Davies both image with 6 inch refractors and they continually show how these high end APOs can cut through the seeing etc and it takes a far larger scope to outperform them. Even then that would be more affected by the seeing.

So much so that Roland Christen has said at times that the sweet spot for scopes is a 6 inch refractor.

The FS152 would be far less affected by the heat issue and that is the guys point.

Greg.

mbaddah

24-07-2010, 07:51 PM

Very informative thanks for that. I think I know what my next purchase will be after my SDM arrives :)

GrahamL

24-07-2010, 10:22 PM

So if the focuser is moved to the opposite side
( I don't get this bit at all )does then the 14.5 "newt kick some butt
on that dinky little finderscope :):D

rmcconachy

25-07-2010, 12:39 AM

I could be completely wrong (in which case I hope somebody corrects me!) but I believe the focuser issue Daniel is talking about relates to where the observer stands versus the direction from which the wind most often blows.

Let's say you live in the continental USA and the wind blows most commonly from the west. Most of your observing time will be spent looking at objects between the southeast, the southwest and the zenith. If, like most Dobs, your scope has its focuser placed on the right hand side as seen from behind the scope then you will spend the bulk of your observing time positioned on the western side of your telescope. While you observe the prevailing wind will tend to blow air warmed by your body across the light path of your scope (through the trusses and across the front). This warm air plume will decrease the local seeing within your scope and reduce the quality of the images you see through it. Of course, the whole scenario is reversed if you happen to be looking at something in the northern sky, e.g., Ursa Minor, and goes to pot if the wind is blowing from a different direction or not blowing at all.

In southern Australia I guess the wind also blows mostly from the west (more northwest in summer and southwest in winter?) but we are mostly looking between the northeast, the northwest and the zenith with our scopes. Therefore the common focuser position is good for this location.

How big a difference the above makes in the real world I don't know. Sticking your warm hand in a scope's entrance shows very obvious heat plumes so that part seems sound, I'm mostly not sure about how consistent the wind direction is, especially in Melbourne! Also, a shroud may help deflect warmed air over and under (rather than through) the scope but it does nothing for any warmed air passing in front of the scope.

ausastronomer

25-07-2010, 04:29 AM

I am yet to see a 6" refractor of any quality that can remotely come close to equalling the performance of a "good quality" 14" newtonian, in any aspect of visual observing, on a consistent basis.

Truth is, a 6" refactor will not outperform a 10" newt, let alone a 14".

Cheers,
John B

gregbradley

27-07-2010, 12:14 PM

I am not that experienced looking through Dobs just at star parties a few times and an observatory and I would have to agree with you there John from my limited experience.

I liked the views from my Celestron 11 GPS. The FS152 was about as bright but much better contrast and sharpness than a Meade LX90 so if that helps position it better. Better views than a Meade LX90 not as bright as a
Celestron 11 but of course sharper and therefore more pleasing but more detail on planets from the 11 inch SCT.

The FS152 was better visually than a Tak BRC250 or a 12.5 inch RCOS but then the large secondary made them somewhat unpleasant as visual instruments giving a dull look to objects (they are designed to be efficient imagers).

Refractors have a lovely look to them visually that isn't quite captured with compound scopes. But of course aperture rules. APO's contrast and sharpness puts them higher than their aperture would indicate. But no good for dimmer galaxies but then is any amateur scope really?

Greg.

rmcconachy

27-07-2010, 09:05 PM

I agree with your message John, a collimated, properly cooled, "good quality" 10" or 14" newtonian will visually beat anything that any 6" scope can do. The refractor may have a `cleaner' aesthetic to the image (which I admit to liking) but the resolution will be less and it will be much dimmer compared to the bigger scope. My post above was trying to explain the `focuser on the wrong side' theory, not suggest that the 6" would show more.

Paul Haese

30-07-2010, 08:47 AM

In an open air environment a compound scope will perform better overall only if the optics are at ambient. Often people talk about refractors being able to cut through the seeing, however one can never really know what the seeing is unless the optics are at or very near to ambient temperature. This is of course where the problem lies. No scope larger than 10 inches will be at ambient inside 4 hours without active cooling. Even with fans the mirror gives off heat for hours.

I have never seen a scope affected by the body heat of a person in an open air environment. It can happen in a dome observatory. The position of the focusor is irrelevant and the real issue at hand is the heat of the mirror.

ausastronomer

30-07-2010, 10:05 AM

That is plain and simply not correct and to be honest it's "old school thinking". It certainly holds true for "full thickness mirrors" but things have moved on a long way from there.

I have an 18"/F4.5 Obsession with a 2" thick OMI mirror and a 14"/F4.5 SDM with a 1.3" thick Zambuto mirror. Both scopes are fitted with mirror cooling and laminar fans. The 18" scope because of it's thicker mirror can invariably take forever to cool and during summer nights at elevation with rapidly falling temperatures the mirror never catches up to the ambient temperature. After a few years experience with the 18" scope and it's cooling properties (or lack of them) I set about setting the specs for the 14" mirror and scope, to address this issue. The cooling properties of the 14" scope, with it's thinner mirror, are world's apart by comparison. The mirror cools so well in fact that I quite often don't bother to run the fans for more than about 30 minutes. Similarly, some of the larger conical mirrors produced by Mark Suchting and Bob Royce in the US address the cooling issue very well.

There were many opinions these thinner mirrors, which are becoming common place today, were astigmatic, particularly when viewing near the horizon. The truth of the matter is this is a non issue if the mirror cell is properly designed and built with a stainless steel cable sling. Further, when I do observe objects low in the sky which is very rare because the air is crud down there, the seeing and atmospheric effects clearly outweigh any astigmatism that might be introduced.

In short, if you design and build the scope properly mirror cooling becomes a much less significant issue. In addition, scope cooling can be further assisted by intelligent storage, transport and scope setup practices. The 14" SDM scope is "easily" the best planetary scope I have used. My planetary scope usage range covers refractors (apo and achro) from 50mm to 378mm, reflectors from 76mm to 915mm and catadioptric and compound scopes from 102mm to 400mm. The 14" SDM with thin Zambuto mirror and 18% central obstruction wins in a canter.

Cheers,
John B

gb_astro

30-07-2010, 10:19 PM

Having read the Daniel Mounsey article it is pretty obvious
that he is not saying that an excellent 6" refractor is, over all, a better
scope than an excellent 14.5 reflector.

In the second paragraph he says:
"When it comes to resolving fine details in globular clusters,
galaxies, planetary nebula, selected nebula and certain open clusters,
the 14.5″ Starmaster wins hands down."

His last paragraph begins with:
"Reflectors are still king for planets and still my favourite choice..."

What he is complaining about is his state of the art Starmaster 14.5, (Zambuto optics, wire mirror sling etc.),
being compromised by body generated thermal currents.

This seems to me to be a valid concern for anyone with an open truss type scope.
Must admit that I have never noticed it but then again I have never looked for it either.
Also of concern is his claim that thermals pass right through current light shroud materials.

Should be easy to investigate:
Orient scope at right angles to wind with focuser upwind, look for thermals through focuser,
rotate scope 180deg with focuser downwind, look for thermals through focuser.

Interesting to get some user reports on this one.

gb.

Peter Ward

30-07-2010, 11:17 PM

There was a very informative piece written in S&T about this very issue, ....well....over a decade ago...I think it was something like "ten telescope myths" probably worth google-ing.

The short answer is aperture rules.

But there are a lot of caveats.

It is a good deal harder...and more costly... to make an exquisite 14" scope compared to say a 6". Apart from the optical figure, mechanical and thermal properties become a good deal more problematic.

And how do you mount a 14-20" scope really well?? Dob? Equatorial? The latter means big money.

That said, a large aperture will always collect more flux and show more detail...the Pro's use metre class optics not because 6 APO are wanting, it's simply because the physics says aperture will put you in different league.

As to whether the observer recognises this is another matter...as the aesthetics, rather than real information, of an image can often give the illusion of a "better" image.

Paul Haese

31-07-2010, 10:05 AM

John you seem to know more about this issue than even Anthony or I. Active cooling is the only way to get a mirrror near ambient. Using the fans you use will get the mirror to about 2 degrees but never to ambient. Have you use a sensor on several areas of the mirror? Laminair fans are not really dealing with the problem and this in your words is just Old School. Some graphed results may change my mind, but there are only a few of us that have done this and I don't recall your name on that list.

Even thin or conical mirrors can take quite a while to cool, Anthony's graphs show that a 14 inch mirror releases heat for many hours even with active cooling. This is less of a problem in coastal areas but in reality what you are saying is well inconsistent to what we have observed and tested.

ausastronomer

31-07-2010, 11:10 AM

Paul,

Anthony takes things to the nth degree for "high resolution planetary imaging". This thread is discussing the virtues of 2 different telescopes for visual use only. What is needed for high resolution planetary imaging and visual observing are in fact worlds apart. I know a lot of people who use large newtonians for visual planetary observations and NONE of them have active cooling fitted to their telescopes.

Paul you aren't remotely qualified to put yourself in Anthony's class. He has been researching active cooling for years and his recent real world achievements speak for themselves. I consider you still have a bit to learn. It is only recently you spent (some would say wasted) a large amount of money on an absolutely superb telescope only to find out after you bought it that it was totally unsuited for the purpose you intended to use it. I could have told you that before you bought it. SDM 14 I believe. An outstanding visual instrument which was never going to be worth a cold frankfurt as an imaging telescope, which was the purpose you bought it for. I believe when you figured out you had made a mistake you subsequently sold it.

http://www.sdmtelescopes.com.au/SDM014.html

Cheers,
John B

Satchmo

31-07-2010, 12:18 PM

I don't understand why the owner doesn't just put a shroud around his truss and get on with life :)

Peter Ward

31-07-2010, 12:29 PM

My truss 14.25" RCOS typically has a 0.6 degree split.... running the fans at 80% power most of the night.

I also have an extractor fan on the side of the dome so ambient air is constantly being drawn in through the dome aperture. It all helps. ;)

strongmanmike

31-07-2010, 03:02 PM

Back in 06 when I still lived at Mt Campbell Observatory (http://www.pbase.com/strongmanmike2002/observatorygeneral) :sadeyes: I and a couple of other astronomers had the oportunity to directly compare views through a Meade LX90 a Synta 6" achromat, a 6" AP Starfire EDF and Meade 12" LX200GPS under rather good seeing.

Result:

The images through the 12" SCT were significantly brighter, faint objects were more easily revealed and under the good seeing the resolution on Jupiter was about equal to the Starfire but the brightness gave the impression that it was easier to see these details, at least this was the consensus (may be wrong of course).

The Starfire images were only marginally better than the 6" Synta, with very slightly more contrast and less colour fringing on brighter things (all expected).

The views of Jupiter through the Starfire were deffinitely crisper than through the larger SCT but dimmer. We could see red spot junior and detail inside the great red spot through both the Starfire and SCT but again the slightly better crispness was there in the Starfire.

Although the star images were not as perfect, we were able to split a 0.6" double star through the 12" SCT but could only manage 0.75" through the Starfire but they were two beautifull white dots with a single broken faint ring around each = optical perfection.

The views through the Starfire, as far as brightness of faint extended objects goes, were about on a par with the LX90 with perhaps a very slight edge to the LX90 when going back and forth between the scopes. EDIT: actually I just went back and had a look at my observing log, of the three observers present, two thought the exrtended objects were marginally brighter through the LX90 the other thought the Starfire (not me) - ie it was that close. Aparently the double star splitting was better through the Starfire (I hadn't recorded what stars we looked at doh!) and all three thought the contrast was better through the Starfire. Worth keeping your observing logs, huh? :thumbsup:

In other words a high quality (the best?) 6" APO is at least as good as an 8" SCT but provides crisper more contrasty views.

I imaged through both the SCT and Starfire and I have to agree with Greg that the overall results through the Starfire are superior to the 12" SCT even with less Focal Length.

These are just observations and far from diffinitive but they are good indicators of how the range of scopes compares generally from an observers perspective.

Mike

marki

31-07-2010, 03:56 PM

Forgive me if I am wrong but Paul aren't you a qualified engineer? I thought I read that somewhere.

Mark

Bassnut

31-07-2010, 04:39 PM

A bit off topic from visual differences..... seems to me the importance of thermal issues are totally different and incomparable to whilst imaging. My 10" (tube) RC has 3 temp sensors and full PID fan control. It gets to less than 1 deg delta between ambient/primary within 20-30mins and the fans then go from full to coasting the rest of the night.

There are so many constantly changing variables in imaging say over a 6 hr period with dozens of subs. eg guiding, seeing, focus, that the thermal current effects of a degree or 2 diff on the primary to ambient is a relatively minor problem compared to all the other factors.

Optical differences aside (ie not counting the tighter images just due to the optics), my 12" non-fanned SCT produced similar results over long imaging runs, albiet with focusing more often due to temp changes.

gb_astro

31-07-2010, 04:52 PM

Mark he does have a shroud but claims the thermals pass right through it.

It looks like the standard rip-stop nylon type shroud.

gb.

wasyoungonce

31-07-2010, 08:04 PM

This thread rocks..I have the popcorn & beer waiting to read the next instalment.;)

TrevorW

31-07-2010, 08:24 PM

I know of one manufacturer who installs micro fans in there refractors to reduce the effects of thermals

jjjnettie

31-07-2010, 08:30 PM

I'm pulling up my chair next to you. :lol:

desler

31-07-2010, 08:34 PM

Pass the nuts and a bottle opener!

D

Hagar

31-07-2010, 08:55 PM

Dougs in the back row throwing Jaffas.

Paul Haese

31-07-2010, 09:44 PM

Ah you clearly know more about all this than we do.

Anthony and I go back 5 years and that was when he first showed me active cooling. In point of fact he and I were discussing this very matter today when we met at Kapunda for a couple of hours. You have no idea what Anthony and I have discussed privately over the years and what design aspects we have thought about.

I have a peltier cooled C14 and had peltier cooling on the SDM too. I am well aware of the virtues of peltiers systems and have taken more data down that you think or espouse.

My SDM was sold because I was living in a unit that I owned at the time and could not use the SDM in my back yard. There was nothing wrong with the scope and yet you infer that there was. The build quality by Peter was to specs I asked for and it was very rigid and tracked better than expected. The only real down side was keeping the planet in the imaging pane. My sale of the scope was not related to what you have suggested here.

You make incorrect assertions and I wonder why anyone actually listens to your nonsense mate. You once before accused me of cutting holes in my SDM and this was utter crap. You have once again made assertions that are totally untrue. However you clearly are the expert and everyone should hail to your truths.

RobF

31-07-2010, 10:14 PM

Are you pulling our leg Trev?

ausastronomer

31-07-2010, 10:36 PM

Well if you go back 5 years Paul you come up about 33 years short of me. I have been "visually" observing the planets with refractors and newtonians for 38 years and strangely enough never felt a need for any cooling assistance other than fans, on any of my scopes. Over the 38 years I have been observing the planets I have had some very memorable views, all without peltier cooling.

What part of, we are talking "VISUAL USE" in this thread are you not comprehending? It's pretty simple stuff really, for mine. You keep babbling about peltiers and active cooling but that is essentially an option for imagers only IMO. If you want to put peltiers on your imaging scope that's good. Your imaging scope happens to be a C14 which is a good choice. It's a poor choice for visual use because of a number of optical and physics issues. However, these do not manifest with imaging, so it is a good choice.

Regarding SDM 14. Simple truth is Paul you bought SDM #14 as a planetary imaging scope. Something it's inherent design does not allow it to excel at. It is a fantastic scope, but not for planetary imaging. I know a large number of experienced people who chuckled when they heard what you were buying and it's intended purpose. You can throw up a smokescreen as to the reasons why you bought it and why you sold it, but truth is I was laughing well before you ever took delivery of it.

Cheers,
John B

Paul Haese

31-07-2010, 10:47 PM

Been into astronomy since I was 9 and am currently 46; I was referring to active cooling and planetary imaging. Not that it is a competition but you seem to think so John. Once again you assume far too much. Just open your mouth to put the other foot in if you like, no concern for me really.

Where are you getting this information about why I sold the SDM? I must have gone mad and now you know my mind. I told the truth about why I sold it, can't be plainer than that. It actually produced the best view of Jupiter than I or Anthony have ever seen through a scope at the first planetary imaging camp. I am sure he will tell you if you ask.

Think what you like John, but each time you make a statement that is wrong about me I am going to let you know that you have come to the incorrect conclusion.

I hope this has been as entertaining for everyone else as it has for John.

Sorry about the diversion for the original thread poster.

ausastronomer

31-07-2010, 11:05 PM

So you should be. You're the one that started dribbling about how fans were inadequate and active cooling was needed, when the thread was only ever focused on visual observing.

Last post on this thread BTW. Better things to do with my time.

Paul Haese

31-07-2010, 11:26 PM

Yes and I clearly needed to be addressed in the manner in which you have done. I must be so deserving of your scorn John.

TrevorW

01-08-2010, 09:27 AM

I suppose thermals was the wrong word more a case of reducing the temperature in an exclosed space as a way of bringing the glass to ambient as quickly as possible

concept

It features a cooling & internal seeing stabilization system:

9 little holes CNC machined on the conical section of frontal aluminum section (dew shield support).
9 little holes CNC machined on the conical section of rear aluminum section (focuser support).
3 internal electrical microfan (speed control provided).

NorthernLight

01-08-2010, 09:31 AM

its like Schopenhauer vs Hegel... and a bit like the two grumpy guys on the balcony in the muppet show.
No offence gentlemen but I truely enjoyed reading.

torana68

01-08-2010, 09:57 AM

so , um, if the dust has settled, forget the Tak and buy a really big good quality newtonian? sounds good to me :) bang for buck I cant see why I'd buy anything but a newtonian or variation of.
NB
a. no degree held (but working on it)
b. been doing it for years, probably more than you
c. "It" wont be expanded on.

marki

01-08-2010, 11:00 AM

Nah newts are rubbish, only good for visual but really who does that anymore? Even an average quality astrograph will show you more then the biggest newt on the best night through an eyepiece. A small refractor with a webcam will eat it alive.

a. several degree's held.
b. started in the womb and I am 107
c. I should hope so
d. I couldn't resist, Just jokes :P

Mark :poke::help::scared3:

Daniel Mounsey

01-08-2010, 02:38 PM

This is my first post on this site. That is correct, the shroud does not protect against body currents, in fact even if you were wearing a thick down coat, it too, would not stop the heat currents. I would also like to thank gb for correcting the number of misunderstandings about my review.

Regards,
Daniel Mounsey

torana68

01-08-2010, 03:12 PM

...cant hide on the net can you :D Mr Mounsey, can you explain, how much do the body currents effect viewing , for me can that be in relation to a purely visual and home/hobby set up.
Is thre a material for shrouds tested to reduce the effect or should we stick to solid tubes where practical? (edit) or are body currents a better option in comparison to tube currents?
ta
Roger

TrevorW

01-08-2010, 03:57 PM

http://www.cruxis.com/scope/mirrorcooling.htm

here guys knock yourself out and go collect some data

Daniel Mounsey

01-08-2010, 04:46 PM

Body currents could effect any telescope if the observer is not aware of it regarding their position relative to the telescope. Open truss dobs are by far the worst. Any type of current is degrading. To the best of my knowledge, there is no shroud available that stops or even slows down body currents. Perhaps someone may come out with a material but this issue is so unknown that even the ATM's who build their telescopes are not even aware of it. Ironic since it's devastating to images depending on the angle. I would definitely stick to solid tubes when practical. They hold collimation better as well.

torana68

01-08-2010, 05:36 PM

ok, i dont own an open tube Newtonian so this is just out of interest, would the degradation be in the order of say 5% at worst (compairing to a theoritical 100% perfect image)? when you say images do you mean visual? thanks for the input.:D
Roger

gb_astro

01-08-2010, 05:45 PM

Daniel, welcome to the forum, although you
must feel like you have just walked in on a bar room brawl.

The usual IIS spirit of co-operation
seems to have have gone AWOL on this one.

I am a bit surprised though that you find a thick down coat
or similar insulation does not reduce the problem.
Logically it should.

(Anyone have a thermal imaging camera? :))

gb.

Daniel Mounsey

01-08-2010, 06:24 PM

I've never really thought of it like a percentage. The simplest way to describe it is to say that an observer can harm delicate images like double stars and planets. It makes the images soft and fuzzy.

torana68

01-08-2010, 07:11 PM

righto, gotcha. thanks for your thoughts :)
Roger

Hagar

01-08-2010, 07:43 PM

Daniel. Welcome,,,, Looks like you must be a bit more precise with your wording. On this forum images refer to camera images and you will incur the wrath of Mr Bambury. He has a definite hatered for imaging of any kind. (Before you sink both feet again John. You were the BIG voice against the IIS Compendium for Astro imagers and had quite a bit to say about the quality of the images shown in this lovely book. Not bad from one who doesn't image.) To be politically correct you had better refer to it as Visual observations.

Again welcome Daniel, but I would have thought the temprature rise accross on open scope with the body close would have only been a microscopic amount and wouldn't have caused aberations as high as the quality of even the best mirrors. It does open up a lot of concerns for me as an imager trying to image through many layers of atmosphere all with differing thermal values.