New GSO 10 inch RC [Archive]

jase

26-11-2009, 12:14 AM

Paul, Don't get me wrong, I'm not personally having a shot at you, but your statement is what puzzles me with these scopes. Given they're so cheap (in true RC terms), these scopes could be likened to being a consumable item. "ah, got a bad one, I'll just go buy another, she'll be right". R&D and QA out of China is surely improving, but is still insignificant when comparing that of US or European manufacturers.

Unfortunately Juliet got it wrong in her statement "What's in a name? That which we call a rose, by any other name would smell as sweet." Not so with RC's and the differing quality on today's market.

If I was to put tongue in cheek, I'd say the results displayed in the link are as good as it gets and worth the money paid. Perhaps slightly out of focus on some images, but others I'd say were in the CFZ. Seeing, sampling and other items may have also played a factor. If I were into these scopes and produced these results I'd be pretty happy. Would I be hoping to get similar results such as those by Roth Ritter who uses a 10" RCA (http://www.optcorp.com/product.aspx?pid=9206) (RCOS astrograph series) and produces work like this (http://www.darkatmospheres.com/scripts/enlarge.php?imgName=portfolios/cosmos/pics/Veil_Western_DAP.jpg) or this (http://www.darkatmospheres.com/scripts/enlarge.php?imgName=portfolios/cosmos/pics/M16_Eagle_DAP.jpg) for example? No way!

No matter which way you look at it, you're pay for what you get. Many are happy with the results and I'm pleased to hear this. I welcome manufacturers entering this market as its good for competition, though the big players have little to worry about with their university and government contracts. Quality comes at price and in imaging, cutting corners leads to compromise. What you do however expect is that the quality is consistent, hence to come back to your original statement, it delivers little in the way of confidence to the consumer. Sounds like a 4k+ gamble, when you could continue to save the pennies for something with a known quality instead of wrestling with equipment each night attempting to pump out a solid image.

Moon

26-11-2009, 06:55 AM

From John himself on the SBIG Yahoo group discussing this (http://www.oneilladvertising.com/Resources/Astro%20Final/Horsehead-LG.jpg)image:

Kal

26-11-2009, 09:05 AM

Well I hope that the 300 that are on the boat to the US have rectified whatever problem was in that pre-production model.

Paul Haese

26-11-2009, 11:27 AM

Jase that is the problem with commercial production I guess. Celestron, Meade and a few others have this very same issue really. I frequently read statements on various forums that people are sending back scopes because of issues with the optics. Yes you pay for what you get. However, I think that US and European scope specialists are charging way too much. This will eventually change though as the Chinese and Taiwanese get things under control.

I am glad to see that this was a preproduction model and that the new one he is getting has been tested by S&T. Personally I would not be happy with those results. Not one image is in sharp focus and I would hazard to say that the results I have obtained so far exceed the linked examples. Not as good as an RCOS for sure but very close to the mark. If you want that extra 10% you need to pay that much more money I guess (not that I agree one should). If I received a 10" like that I would send it back without any question.

jase

26-11-2009, 01:41 PM

Its all relative Paul. I'm not going to deny that the US and European manufacturers are expensive, but they are also spending at least six to eight fold in time to build scopes compared to the Chinese or Taiwanese counterparts. As you say, the latter is mass produced, quantity over quality philosophy. Robotic arms instead of flesh and bones driving greater profit, but improved quality? hmmmm maybe with time?

So who wins? You buy one of these scopes, have to spend more money and commit your time to resolving matters which should have technically been addressed through R&D and QA. You've had your fair share of troubles as have others and I'm sure this has come at a cost. Alternatively, you pay more for an established instrument and get close to a turn-key imaging solution, be it minor tweaks to get it humming along. If the Chinese or Taiwanese manufacturers spent a similar quantity of time as the others, prices would climb, so its a trade off.

For the money that is out laid, the results are what I would expect and as such I'd be happy. Obviously everyone has different expectations. Whether they are realistic and obtainable is another discussion. With such a vast difference in quality between budget, mid spec and top end RC's, one can only compare results of a similar breed RC, so my previous post in reference in the 10" RCA is moot. The RCA series and those from deepsky instruments are mid spec instruments as opposed to the budget RC's coming out of China or Taiwan. What I was attempting to allude to however is that paying that bit extra can yield vastly different (superior?) results.

I want to be clear that I'm not attempting to put people off purchasing budget RC's. In many cases, they'll probably meet your goals and you will be happy with the output. There is a strong market for such instruments which will thrive with time. I do however suggest people review the facts and manage expectations. Comparing the differences between a 4k and 12k instrument can be the difference between night and day, no matter how much time and money you sink into getting the 4k instrument working. Its putting lipstick on a pig.

Terry B

26-11-2009, 03:00 PM

I wonder how one of these scopes would compare to a Vixen VMC 260L?
They retail about $500 more but have the Vixen quality behind them.

pmrid

26-11-2009, 03:13 PM

Hi Mark. has anyone done any comparisons between field flatteners that suit the 8" RC?
Peter

bmitchell82

26-11-2009, 03:18 PM

:lol: hahaha lipstick on a pig, :) reminds me of those.. whoopsys i wont go there :D

rat156

26-11-2009, 04:52 PM

I think that some of the points made here deserve closer scrutiny. The "quality" of images depends on much more that the quality of the optics. Firstly we should define what we mean by quality of images. There are some measurable parameters which I generally grade images, in particular sub-exposures for inclusion or exclusion in a final image.

The first thing I look at is the roundness of the stars. This is mainly influenced by the tracking of the mount. Barring any optical faults the roundness of stars on RC's af any brand are really good. The GSO RC has excellent roundness all the way to the edge of the field of my ST-10. I don't have an expensive RC to compare with, but there are many images to which I can compare. The quality of the optics are relatively unimportant wrt star roundness.

The FWHM of the stars, particularly a change between the centre and edge of the field. This can be influenced by many things, focus is king though, if the GSO is in focus I believe that it will produce stars with the same FWHM as any expensive RC. By far the greatest influence is your local seeing. The quality of the OTA will influence focus, as if the camera can be easily skewed, or the focuser is not up to taking the weight of the camera then this will make focus difficult to obtain and then hold. This is easily remedied by an aftermarket focuser, so add $500 to the cost of the GSO. If you know beforehand this is no big deal. I would not expect any of these problems with an expensive RC.

Optical defects can occur in any scope. They should not be allowed out of the factory, whether that be a big or small factory, obviously the more you make the more likely that one will slip through. GSO have proven to be very good about taking returns of defective scopes and replacing them. Astigmatism and field curvature are properties of the design, not how well the optics are made. The Strehl of the expensive scopes is almost certainly higher than those of the GSO scopes, but how high do you need to go?

Image depth is certainly one area that the optical quality of the scope can influence. Do the images produced by the expensive RCs have greater contrast? Is this more likely to be due to more longer, deeper subs from dark skies? I say yes and yes to both of these questions. I find that when the image contrast of a picture is greater than mine the photographer has taken more or longer subs. The scopes vary from refractors to various reflectors. The main problem with comparisons is that owners of $10k+ scope generally have them at dark sky sites on super mounts, not like the rest of us from a suburban location on a not quite so good mount.

I'm not saying that the expensive RC's are a waste of money, but for 5-10 times the money of the GSO variety they should be like chalk and cheese. They are not.

For the money you can't do better IMHO, bring on the 10", I can't wait, then the 12" version. If they are rubbish we'll know soon enough and I'll just have to make do with the 8" version.

Cheers
Stuart (Smearing lipstick on Bacon)

Zaps

26-11-2009, 05:04 PM

This reminds me of the arguments of the Astro-Physics fanatics back home. For them it was Astro-Physics or nothing, no matter how much logic and reason was proffered. Yet I have to think that if Astro-Physics wasn't an American company, those same fanatics would have no interest in it.

At least 99% of their stance was based on patriotism and flag waving. Most of them never let their precious telescopes leave their den or dining room anyway. That is if they hadn't already sold it and made a profit before it was delivered to them.

For the record, in my opinion, there aren't many $12000 telescopes that are $8000 better than a $4000 telescope. There may be none that are $8000 better. Looks like some people don't think an $8000 brand sticker is overpriced, I guess.

But speaking for myself, I'd happily save that money and buy a "junky Chinese made clone", then slap a few upgrades on it. The end result is a telescope which performs as well as a dining room display model but for a lot less cost.

Paul Haese

26-11-2009, 05:35 PM

ROFLMAO. Mate that takes me back to my time in Sydney as a lad. Don't worry I'll tell you some time.

I am well aware that eventually I will buy another telescope to further my goals. I fear though that many premium telescope makers will eventually outprice themselves and leave their scopes to the rich man just as it was years before.

TrevorW

26-11-2009, 06:10 PM

I've so far kept quite but just can't help myself:

1. I'll never unless I win Lotto afford an El Capitian or RCOS or an SBIG 11000 SXYZ top of the range camera
2. I may be able to afford a reasonbaly priced G11 and similarly priced CCD Cooled camera some time in the future
3. So far the problems with my images have been depth, noise and roundess of stars plus the inevitable tracking induced elogation errors etc
4. and lets not forget that the seeing conditions play an all too important part in the final image quality

However is saying this like others I have rec'd favourable responses from numerous people on a number of forums on the relative quality of my images (please don't take this as bragging cause I'm not)

So improving on the obvious faults in the long run should lead too far better images.

Whether you spend $2000 or $20000 on the optics if the other variables ain't right it ain't going to make an ounce of difference.

So for those who can't afford a RCOS, Star Instrumnet or Planewave then the GSO RC's offer an affordable alternative as far as I'm concerned.

gregbradley

26-11-2009, 06:38 PM

I've been impressed by some of the images from the 8 inch. Paul has shown that. If you can sort that star elongation at the edges your laughing. A flattener of some sort should do the trick.

They do represent good bang for your buck, kind of like a Subaru WRX telescope.

The Vixen VMC260 is an interesting competitor. I'd go the Vixen as the trend nowadays is for corrected compound scopes like ASA Newts with the Keller corrector, Planewave CDK with its doublet corrector, Ceravolo
corrected Dall Kirkham, Hyperion - corrected Cassegrain. The A&M RCs are good bang for your buck too for a carbon truss RC but they also need a flattener that they sell. They also have a nice reducer. So does Planewave now. This area of the market is heating up with Meade ACF and now Celestron HD optics. There's a lot of choice and some very nice gear on offer.

These RCs all need flatteners to sharpen up their star sizes off axis although the 12.5 inch RCOS I had did very well without it.

Greg.

dpastern

26-11-2009, 09:30 PM

If I didn't know any better, I'd say that there was a slight focus issue, and some warping of the imaging plane in his images. Compare it to the other Astrograph images from the other 10" manufacturer that he's testing and you'll see that they're sharper, more tightly focused and less elongated.

I'm thinking possible figuring issues with the primary and secondary, with innaccurate (ever so slightly) distances between the 2.

Dave

Peter Ward

26-11-2009, 09:36 PM

Dealer hat off for a bit...

What many people don't get is: with any engineering, the first 80% is pretty easy.

For example, GSO make a fine product as it represents great bang for buck, but frankly they are not an RCOS or AP.

Think of audiophile systems (I rather like JBL or Klipsch monitors)...or cars (I have a penchant for stuff from Stuttgart and Prancing horses ;) )

The reality is most Hi-Fi's give you a good sound, or cars a comfortable ride from A to B

But it you want flat line 20-20KHz audio, or 0-100km in under 4 seconds....it *costs*

Why is it a revelation that with optics *you also get what you pay for*?

Sure, with anything that lends itself to *consistent* mass production quality can go up for a lower cost...but machines can only do so much.

You might buy a Casio watch that is good to 1 second per month. Yet the next one of the shelf is only good to 2 minutes....the question is: is it reasonable to expect 1 second accuracy? A Breitling is guaranteed to give you that 1 second, plus a really snazzy case, and then some...but costs 10-50x more.

The GSO RC10" scope will not be unlike the current RC8", but with a bit more aperture and FL, and I'm sure for many will fill that "sweet spot" of price/performance .

But if you want that last 2%.... just move along :)

So endeth the lesson. :)

dpastern

26-11-2009, 10:42 PM

Peter - few speakers go down to 20hz I'm afraid. Most roll off around 35hz. Certainly, smaller, studio speakers, do not go down this low, they do not have the volume to produce the longer wavelengths for such low frequencies. And it's not so much the higher frequencies - 20khz isn't hard to do itself, it's how it's done. Odd or even harmonic distortion?

And yuck to JBL or Klipsch I might add.

Sorry, just couldn't resist since hi fi is another hobby of mine.

Dave

Peter Ward

26-11-2009, 10:56 PM

Heretic! :)

Klipsch Corner horns (do they still make them??) *do* go down to 16Hz ......slightly higher for my JBL 4315 Studio Moniotrs (no longer made).
(fingers in ears) I will not hear *any* critique of these classics!

Newer is not always better!

Kal

26-11-2009, 11:01 PM

Since you want to bash AP I'll provide you with a few words from Roland to ponder, and ask why exactly are these chinese made RC scopes popular? Is it because of the performance, or is it simply because everyone see's expensive RC's and want these chinese made ones simply because they are relatively cheap?

source (http://www.astromart.com/forums/viewpost.asp?forum_post_id=670406&poll_id=&news_id=&page=14)

dpastern

26-11-2009, 11:25 PM

Uggh my bad Peter, you are, of course correct - Klipsch horns, like most horns will go down that low. To be fair to me, you didn't mention horns in your original post, you said monitors (they are 2 different things lol as we both know!!!).

My REL subs go down to around 12hz (-3db) when positioned properly, and in a decent room (which is also large enough to handle the larger wavelengths). Sorry to hijack the thread lol!

and old isn't necessarily bad, I never said that. I still prefer LPs to CDs. And valve amps to transistors.

Dave

Zaps

27-11-2009, 05:26 AM

Friend, nowhere did I "bash" A-P. Maybe I did bash the attitude of Astro-Physics fanatics, but honest folk admit they deserve it, because what goes around comes around. ;)

What I did say was that few if any $12000 telescopes are $8000 better than any $4000 telescope. I guess when someone's paid that much money they don't want to know or believe that a $4000 is as good, or almost as good as their $12000 telescope. And if that $12000 telescope never leaves the display wing of the buyer's home then the buyer should keep his mouth shut about the merits of other telescopes which are probably out in the field being used. If the buyer is just another flipper, then they definitely have no place criticizing the telescopes of others.

You don't see a lot of that display-or-profit mentality here Downunder, but it's the most common one in the USA when we're talking about Astro-Physics telescopes. To each their own, yes, but those collectors and flippers are also the most vocal critics of other manufacturers, which says a lot about the artificially-generated mystique of Astro-Physics stuff: A ten to twenty year waiting list for small refractors or compound telescopes? Gimme a break.

Take an "inexpensive" off the shelf telescope, maybe of Chinese manufacture. Add a bunch of aftermarket accessories, like a Moonlite or Feathertouch focuser, etc etc. Pretty soon you have a telescope with optics not far short of a $12000 telescope, maybe even equal to one, and the nice mechanicals to boot. How much did that cost? How long did you have to wait for it? How much pleasure and use are you getting from it out under the stars while the $12000 boys are inside inspecting their OTA with a magnifying glass looking for dust motes? :question: :lol:

Kal

27-11-2009, 08:33 AM

I've been a member of cloudynights as long as I have been a member of iceinspace. I'm also a regular reader of Astromart forums, where all the bigwigs of astronomy manufacturing post. I'm a member of more yahoo groups than I care to remember. This stereotyped AP owner that you talk about is not a common thing. I saw a guy sell a takahash TOA-150 that was used once and only 3 months old the other week. I guess if that was an AP owner they would instantly be labelled a flipper. Yes there are flippers out there, but if you search how many GT's have been sold or auctioned on amart then you will not even find a dozen, and Roland is onto making his third batch right now, so there are 200 out there in the hands of owners. Less than a dozen sales, even if we assume all are flippers, means that 95% of owners are happily keeping their scopes, and I'm sure there are far more of those being used than being displayed in dining rooms as trophies.

Getting onto my second point, you still didn't mention why you thought these chinese made RC's are popular. I still contend that if it wasn't for the $10K+ RC's made by the likes of companies like RC optical, then there would be zero market for these cheap RC's. Their popularity is driven by consumerism wanting something that is generally expensive, simply because it is cheap. Their popularity is not driven by their performance. That does not mean that they can't perform well, but I still question why these 300 on the boat to the US will likely sell like hotcakes when the only astrophotography I have seen by them shows bloated stars.

Moon

27-11-2009, 09:07 AM

It looks like the push-pull screws on the back of the 10" have moved out towards the edge:
http://www.atscope.com.au/gsorc10scope.html

Compared to the back of the 8" where they are around the focuser.
http://www.gs-telescope.com/content.asp?id=149

dpastern

27-11-2009, 09:56 AM

The 10" isn't carbon fibre?

Dave

Paul Haese

27-11-2009, 10:04 AM

Kal bloated stars is not a function of the optics it is a function of the sampling. I have 0.68" per pixel and the stars appear bloated. Peter took an image of the lagoon earlier in the year with a STL11000 and his sampling rate is much better with that camera and the stars had nice non bloated stars. He is a skilled operator and the image looked just like any other RC image. It is the camera verses the focal length that produces stars like that. Refractors suffer from the same thing.

The reason these scopes are popular is that they afford sharp views for the image scale. It is next to impossible to buy a refractor at present that gives the same image scale for galaxy imaging that an folded design can. If a telescope can give sharp views and do basically what you want and it is cheap are you telling me you would rather pay more money for a telescope that cannot do all that??? I have looked through an AP or two and yes they are nice but they are no better than a Tak and at least they are cheaper and you can get them sooner. I agree with Zaps a 10 year wait list for 6 inches of aperture at best is well odd. I can sense a lot of fear in your post about Chinese imports. The gear coming out of China and Taiwan now is very good, and it is affordable to the average punter. That is why people are buying them. It means you can get a descent astrograph without having to save for years, and that is not to mention all the spare parts one has to buy that are expensive too. I think it is a good thing that people want them, they want affordability.

Satchmo

27-11-2009, 11:04 AM

I would have thought bloated stars were due to a number of possible factors including optics, guiding, collimation , seeing conditions , processing , mount stability and sampling size, and could be a complex mix of all of these things. Would a Kodak KAF 8300 chip be better choice to get sharper stars due to small pixels and large numbers of them .

Paul Haese

27-11-2009, 11:08 AM

Just to illustrate my point about bloated stars here are some from the AP gallery. Seems some of their scopes are perhaps defective due to bloated stars.

Image one (http://www.astro-physics.com/gallery/astroph/jgleason/vdB-142jg.htm)

Image two (http://www.astro-physics.com/gallery/astroph/rgralak/pelicansmallrg.htm)

Image three (http://www.astro-physics.com/gallery/astroph/pward/coronaaus.htm)

Image four (http://www.astro-physics.com/gallery/astroph/rgralak/m42rg.htm)

Pixel size makes a huge difference to how stars are shown on any image.

Paul Haese

27-11-2009, 11:12 AM

Mark yes there are lots of factors which cause bloated stars. However the KAF8300 chip has small pixels which causes over sampling and this commonly (all other things being equal) causes bloated stars. DSLRS also have small pixels too and this also leads to bloated stars. Most of the images taken so far have been with camera's with small pixels. Stuart being the exception at present with the ST10

If the optics are inferior then all the stars will have a bloated appearance not just the brighter ones Mark.

mick pinner

27-11-2009, 11:34 AM

does it seem to anyone else as it does to me that some equipment manufacturers must be sitting back smiling.
people are buying cheap or affordable gear, call it what you will and then when it doesn't perform up to expectations spend more money to rectify the problem or make excuses that oh well it was cheap.
in the case of the GSO RC, given that some people have pointed out it's shotcomings should not the manufacturer give more information as to it's optical ability so that people know exactly what they are buying.
surely if they are doing the research and manufacturing then they are aware of the problems before they hit the market place.

Kal

27-11-2009, 11:48 AM

Paul, my point is not to compare the GSO RC to an APO refractor. Instead I am comparing the GSO RC to a simple newtonian with a coma corrector, which can produce results just as good and at a comparable cost. But a newt with a coma corrector doesn't have the marketing jazz of an RC scope. The main reason why these scopes are popular is because of the $10K+ brand name RC's, and because people have a perception of them being cheap, not because of the results that have been obtained.

If I want a cheap scope that will give me good performance to the corners of a KAF-16803 chip (http://www.flickr.com/photos/26671216@N02/3570358333/sizes/o/in/set-72157618792310067/) then I'll spend US$1399 (plus eschew and shipping costs) and get a simple SCT with a built in flattener (8" Edge HD). And I know that I won't have to crop corners from the STL11K like peter did, or worry about trying to get flatteners to work to realise the potential of the design.

Hagar

27-11-2009, 02:34 PM

Paul, I don't know why you bother to justify your purchase each and every time the GSO RC is spoken about. There is a football field of people just sitting on the side lines ready to pounce on your every word.
Looking at the images you have produced with your 8" GSO you have nothing to answer to. If some of the would be experts could produce the same or better results with their big expensive scopes I could see some areas for their comments but to be honest the results all stand in your favour.
By the way. I just ordered an 8" based on your results and the great image scale produced by the scope, not because it is like an expensive scope or brand name display item. Mine will also be used.

Peter Ward

27-11-2009, 02:44 PM

Humm...while I thought it wasn't bad at the time...that Corona Australis image is rather dated....not a great example.

Peter Ward

27-11-2009, 03:15 PM

Nope and a little bird tells me the first ones will arive in Oz in the first week of December.

Paul Haese

27-11-2009, 03:19 PM

Yes more information should be made available on the GSO website which is at best amateurism in content. The manufacturers have listened to the reviewers and made the changes to peripheral equipment. The optics I have never found to be problematic, but a spot diagram on the site might be useful.

I beg to differ, your comment was clearly aimed at saying the stars are bloated on the GSO. I was just pointing out that if everything is equal the pixel size makes a difference to stars even in an AP.

You are of course right Doug about why I bother and there is a plethora of people willing to take me up on my comments. ;)
I am humbled by your remaining comments. I just keep trying to get better and better at my imaging as you well know. I am glad that my efforts have not gone un-noticed. Thank you very much. These are good scopes and if you want to ring when you get the scope by all means do.

I was not intending to insult you Peter, only trying to show that equipment relating to pixel size could be a limiting factor. Your skills have come considerably a long way since then and many of us look to your images now as inspiration and an example of where we should be heading.

Paul Haese

27-11-2009, 03:27 PM

That might be a problem though. The 8" is very stable and almost never needs to have focus changed during a night once cooled and set. In fact I often find that focus is good from a previous session. Have GSO given an explanation for why they are not using carbon fibre tubes? I was considering getting one but with a ali tube I am less than interested.

Peter Ward

27-11-2009, 03:41 PM

I never saw it that way...Absolutely none taken! :)

Peter Ward

27-11-2009, 03:46 PM

Two honking great aluminium Losmandy dove rails running from front to rear cells would be my guess...having a low expansion tube would be of little benefit other than a nice look.

Bigger scope, larger mass, more thermal inertia, so a metal tube would also cool a little quicker. BTW I thought the fans were a nice touch :)

dpastern

27-11-2009, 04:00 PM

I thought the idea of the CF tubing was to help with thermal cooling? Larger mirrors take longer to cool, ergo stable cooling/currents etc would be an even greater must with a larger scope? Or am I completely wrong in my logic?

The fans do look pretty cool, I presume a fixed RPM? How are they controlled?

Peter, do you feel that bloated stars are a result of poor focusing/focuser slop/poor optics or just poor CCD/OTA + FL matching? In all honesty, I don't think I've seen a GSO RC based image that looks ultra tight, if you know what I mean? Pinpoint stars...user fault or something more?

Dave

rat156

27-11-2009, 04:01 PM

I have bloated stars?

http://www.iceinspace.com.au/forum/showthread.php?t=52898

Show me a sharper image taken at the same image scale with an amateur scope, then I'll believe you.

The FWHM of the stars in the image was around 2.5" from memory, which is pretty much what the seeing is typically at my place. Like Paul has mentioned the star size is a combination of factors, optical quality of the scope being about third most important as long as its a reasonably good scope.

Cheers
Stuart

Kal

27-11-2009, 04:25 PM

I was referring to the 10", which as I said, will probably still sell like hotcakes even though the only images I've seen through the scope (granted it was a prototype) which were linked earlier in this thread had bloated stars.

Nice pic BTW.

Kal

27-11-2009, 04:43 PM

It is around the other way. CF actually insulates, which interferes with cooling on closed tube designs like celestron SCT's, but with the open tube design of the GSO RC it doesn't have an impact on mirror cooling. The advantage of CF is that it can be bought as a zero expansion material, so if you use zero expansion glass to make your mirrors with, you won't have focus shift as the temperature changes through the night.

Peter Ward

27-11-2009, 04:50 PM

No, CF is used due its low co-efficient of thermal expansion. Being a composite however, it doesn't conduct heat very well & takes longer to cool.

Too many variables to know why some images are not great (regardless of the design or make). I wouldn't automatically blame the 'scope when seeing can easily be far more caustic to an image.

dpastern

27-11-2009, 06:05 PM

Thanks Kal & Peter. If you don't ask, you don't get answers. :)

Dave

gregbradley

27-11-2009, 07:11 PM

Does it still have a carbon fibre tube?

Greg.

gregbradley

27-11-2009, 07:17 PM

Yes I agree, Pauls images are excellent. The little remaining problem of corner star eolongations could be handled with a flattener. I am not sure that flatteners are that sensitive to different focal lengths (no doubt within limits). For example I use a Tak FS152 flattener designed for a 1200mm APO on my AP140 at 930mm and it works perfectly.
APM sell a generic flattener and Televue have their reducer/flattener.

If you have a flattener for another scope it would make a good experiment to see which fits it.

And take heart this is no criticism of the GSO RC as expensive RCs need flatteners to some degree. A&M RCs apparently really require them.
Just goes to show the formula really is 2 mirrors (a largish secondary) and a corrector/flattener for astrophotography.

Greg.

Grahame

27-11-2009, 08:17 PM

Greg: As per Peter's post they are back to an aluminium tube for the 10" (see http://www.atscope.com.au/gsorc10scope.html for picture)

Grahame.

marki

29-11-2009, 04:26 PM

Interesting, andrews still has them listed as having a CF tube.

Mark

AlexN

29-11-2009, 04:58 PM

The few guys in the US that got some from NEAF earlier in the year got CF tubes... I dont think they would go to an Aluminium tube after already producing CF tubed models for NEAF? I could be wrong, but it seems unlikely.

gregbradley

04-12-2009, 03:33 AM

Aluminium tube wouldn't be the end of the world but carbon fibre would be so much superior. One of the attractions of CF is stable focus.

My RCOS 12.5 inch with carbon fibre tube would retain the same focus point night after night. Amazing really.

However with colour "parfocal" filters being not really totally parfocal best practice would still be to refocus for each filter when imaging.

But if you use CCDsoft and you program in an imaging run of LRGB for 6 hours throughout the night its nice to know the scope will hold focus despite temperature shifts and perhaps you don't mind the slight difference of focus on RGB (its often very close but not perfect - ie Astrodons and Baaders, Astronomik filters).

Greg.

Paul Haese

04-12-2009, 10:21 AM

I have to agree, my RC retains focus for nights on end. I go and check and there is not shift whatsoever. Carbon fibre is the way to go. Eric at the ASSA meeting the other night thought that going back to metal tubing was a budget issue. Carbon fibre tubes cost a lot to make. To me this is a mistake to not include carbon fibre tubes, they could raise the price a bit to cover the cost and everyone would still be happy.

Peter Ward

04-12-2009, 02:23 PM

I've been advised by GSO that a carbon fibre tube would add around $A1000 to the cost of the RC10.

As I mentioned earlier, the front and rear cells of the RC10 are connected by two Aluminium Losmandy D-type plates.

These have no expansion joints and are bolted on tight....there is no way a CF tube will be any benefit in that configuration, other than perhaps being a tad lighter/stiffer.

RCOS mount their secondaries very differently, in either the carbon fibre turss or tube configurations only CF is used to mount the secondary, with no aluminium plates inbetween.

CF is also not the best material for refractor tubes. None other than Roland Christian at Astro-physics noted that a lens will shorten its focal length as it cools, hence aluminium tubes help compensate for this effect (by also thermally contracting)....this would not happen with CF.

Moon

04-12-2009, 04:10 PM

From Andrews (http://www.andrewscom.com.au/site-content-section-10-guansheng.htm#cassegrain):

dpastern

05-12-2009, 12:09 PM

Interesting.

Dave

Hagar

05-12-2009, 01:29 PM

Sounds to me like an excuse to increase the price considering the original specs for these scopes was to have a carbon fibre tube at the cost of the aluminium tubed version. The original prototypes came out with CF tubes.
Probable reason for the Al tube was to get the scope out before Christmas while waiting for the CF tubes to be manufactured.
CF is now a relatively cheap material and costs nothing like it used to cost some years back.
A classic example was the fishing rob industry. CF fly rods were only manufactured by premium rod makers at huge costs $1200+ for a 9' fly rod. With improvements in manufacturing techniques similar CF rods are now made for $150.

mick pinner

05-12-2009, 01:57 PM

l agree Doug, $1000 extra for a C.F tube is utterly ridiculous regardless of it's precision.

dpastern

05-12-2009, 02:29 PM

Get used to it boys, it's called "profiteering". Apparently, in the name of 'free markets', it's acceptable. And it's socially unnacceptable to criticise it.

Dave

AlexN

05-12-2009, 04:36 PM

buy the Aluminium one, convert the optics into a carbon fibre truss tube.. add a couple of grand for an instrument rotator, a FLI PDF focuser and some heaters to keep the optics dew free and then go photon bashing!! :)

cventer

09-12-2009, 12:13 PM

Anyone got theirs yet ? I got note from Peter saying shippment had arrived but curious if anyone has it yet and what reports are on scope ?

Peter Ward

09-12-2009, 12:37 PM

:doh:

Admittedly these are a little fancier...

http://www.dreamscopes.com/pages/tubes-honeycomb.htm

Note the 12" OD tube price....$USD 1400

Waxing_Gibbous

09-12-2009, 02:13 PM

According to my business partner who is an actual, university graduated, certified, been employed by BAE aerospace and McLaren, composites engineer and licensed composite construction inspector,(smartarse), Mr. Christen is correct.
As CF does not expand or contract (to any meaningful degree). unless weight is the primary factor, any gains in rigidity will be outweighed by possible distortion of the optical train. This should not really be a factor at <130mm, but above that, it will start to become noticable unless the lens / mirror cell is well isolated. Preferably in Al or Ti which have roughly the same expansion properties as most glasses used in telescope making.
The larger the lens or mirror, the greater the effect will be, by optical standards anyway, you wouldn't notice it in real life.
Also it costs roughly the same to produce a CF tube as an Aluminium one, depending on the quality, but the rejection rate is higher with CF (bubbles and such in the resin etc etc), hence the higher price.
I'll take his word for it.

Peter Ward

09-12-2009, 02:47 PM

While this *might* be true for small OD tubing a quick web search of CF suppliers shown this is not the reality for larger OD's. eg.

http://www.carbonfibreexpress.com/index.php?cPath=22_41

I suspect there is not a great demand for large diameter CF tubing, as can be seen above, a good length of 70mm OD runs around $US960.00 .
300mm OD is not even listed.

Waxing_Gibbous

09-12-2009, 03:18 PM

Sir is partly correct. If this humble servant can find the flippin' website, this humble servant will direct Sir to a firm that makes CF tubes for the oil & gas industry, where this humble servant notes there is rather keen demand for bloody-great CF tubing, begging Sir's pardon of course.:D
These, this insignificant worm, dares to point out, are a lot more rugged and and a darn sight cheaper ( about 1/2) than those available from "boutique" composite manufacturers.
This unworthy one will post the URL as soon as this unworthy one can find it.

Peter Ward

09-12-2009, 03:40 PM

Sorry, I don't get the need for sarcasm.

You'd probably need around 2mm wall thickness, 300mm OD...and given you'd probably not want your telescope to look like an industrial oil pipe...a nice high gloss cosmetic finish.

As I mentioned way earlier...GSO can get them, but the OEM cost will add around $US700 to the price per OTA....given the benefits, a needless expense IMHO.

If it was $100-200 it would be a no brainer... the CF version would look cool if nothing else.

Waxing_Gibbous

09-12-2009, 03:55 PM

Wasn't sarcasm. Sorry.
Actually some do have a nice high-gloss finish, inside and out, - normally white, zinc based coating as they spend most of their life in the sun.
The other stuff they use for drilling is not as nicely finished, but still pretty good.
My point being you don't HAVE to shell out a fortune for good CF. But really, Aluminium is as good or better for most applications.

AlexN

09-12-2009, 05:23 PM

A mate of mine and I were discussing this just last night, the thermal expansion/contraction of an aluminium tube the size that we would guestimate the GSO RC10 has would be, Given a 20°c temperature change, the worst case scenario (assuming very poor quality Aluminium) was a contraction 45 microns.

The F/8 optics of the GSO RC10 give a CFZ (Critical Focus Zone) of 140 microns. Hence, given you focus well at the start of the imaging run, and don't experience more than a 20°c drop in temperature during the imaging run, your focus would not noticeably drift over the course of the run... Its a different story when you're imaging with a fast system, Ie, an F/4 scope with a CFZ of 35 microns.. but with the slower ratio's, your focus would very rarely shift.. not before you hit the meridian and have to flip the mount anyway, at which point, how hard would it be to just touch up the focus before recommencing the run after the flip?

Yes, CF would be lighter, Yes it would likely (depending on quality/thickness etc) be more rigid.. As Peter said, It sure does look cool... but will it make a noticeable difference in focus during the course of your average imaging run... Probably not...

If we were talking about a fast refractor, MAYBE. but then, even the glass in the objective lens will contract/expand during big temperature changes, causing the focus point to shift anyway, regardless of what the OTA is made of...

Yes Saying "0 focus drift due to temperature is a great way to sell telescopes" In most cases, it actually MEANS nothing...

Bassnut

09-12-2009, 06:01 PM

I have 2 OTAs, one Aluminium (12" SCT), the other CF (10" RC). The Aluminium tube requires focusing every time I use it and during a typical 6 hr imaging night. I usually dont bother refocusing during the night. The Aluminium tube SCT sub stars get noticabley blobier as the night wears on, especially if there is a large temp change.

Even though I always focus the CF RC on start up, I notice say with a typical 20000 count focus position, the new focus is never more than 10-30 counts off, and there is no visible change. The focus also does not change visibly during the night. Weeks can go by, with large temp changes, and the focus does not change visibly on reuse.

Unless there are other reasons for the SCT focus to change (the mirror is always hard locked, never changed), anecdotally at least, it seems to me, the CF tube is much better. Apart from other differences in these 2 OTAs, the focus in subs are always more consistant with the CF tube.

Having said that, with regular refocusing, the aluminium tube is fine, but unless you are fairly keen or have automated scheduled autofocus, regular manual refocus during long image runs can be pretty tedious, this is where the CF tube becomes very handy.

bmitchell82

09-12-2009, 06:09 PM

just something small fred, i notice you have a RCOS 10" and a Meade lx200r... they are in two totally different leagues! Meade made in mexico RCOS are hand made instruments (so im lead to belive). its like saying a skywatcher can proform just as good as a Takahashi Mewlon..? just my thoughts on that matter!

Paul Haese

09-12-2009, 06:23 PM

I reiterate and agree totally with Fred. The 8" I have has not had to have the focus changed in 4 imaging sessions. I check of course on each occassion and mid way through the run check again. It just does not move. My Tak scope on the other hand has to be focused each session and has to have it changed during a session on some occassions. Coefficiency of linear expansion would suggest a metal tube will move if the temperature changes by as little as 5 degrees and it progressively moves more and more as the temperature changes. 20 degrees will have quite a large change in focus. Personally, I would be prepared to pay the extra.

Bassnut

09-12-2009, 06:26 PM

Well, I was tring to avoid the brand thing, and just talk about focus consistancy (not absolute focus, which granted is tighter on the RCOS).

There well maybe other reasons for the focus change, I dont know, cant see any.

The focuser I use on the Meade has temp compensation (TCF-S), which I never bothered calibrating, dumb I know, call me lazy, would probably solve the problem in one hit.

In the end, the diff bettween aluminium and CF is there and significant IMO, but can be overcome with care or a temp compensating focuser. Whether the cost difference is worth it is another story given focus drift can be overcome, but as Peter says, its the last mile that costs...... And the convienience of no drift CF to start with sure makes imaging more enjoyable.

bmitchell82

09-12-2009, 06:42 PM

That granted the CF doesn't fluxuate with temperature like ally. but if you think that it only moves in one direction it doesn't it will bloat the OTA as well as increase its length. now theres your problem what is the back of ota made of? and the focuser tube?

there was a really good youtube presentation on a guy with a 32" Relay cassigrain look for the link in the forums. now he shows where you need the Zero shift though careful design. and it didn't stop at the tube (he was using a CF truss setup) and a aluminium primary mirror box, but the link between the mirror box and primary mirror fixing was CF. Zero shift! and carbon fibre in the secondary-primary mirror tubing admittedly there was a series of lenses mounted within. If you want to go that extra mile you should have your odometer calibrated, no use saying ive gone the extra mile just because the odometer says so. whoops i had mini minor wheels on my tractor?!:thumbsup:

oh and for a bit O info here is a little link for non belivers.
http://www.engineeringtoolbox.com/thermal-expansion-metals-d_859.html

Kal

09-12-2009, 08:28 PM

That contracton of 45 microns will be far more pronounced in a two mirror telescope. It is not a simple 45 microns at the focal plane, it is a difference in seperation of the two mirrors by 45 microns, which will shift the focal point by a much larger number (unless your calculations were far more complex than I give you credit for!!!)

bmitchell82

10-12-2009, 12:18 PM

andrew your still missing the point. you have a CF tube cool. what comes out the back of your telescope is aluminium.... and if im not mistaken RC's inherently have a whole lot of back focus so that you can add in your filter wheels OAG's field flatteners ect ect ect.

You just shot yourself in the foot because what you just took out over there is still over here.!? I smile every time somebody does something and thinks they have eliminated it and then preaches to the world. do the whole lot properly and then you can say you have eliminated it as i stated in my previous post.

As for 45 micron, can you honestly show me what 45 micron looks like? ill tell you now that 45 micron is BLOODY SMALL. and to give you a point to think about when talking about microns, what focuser do you use? if your using a manual focuser you make me laugh as i will 100% know you haven't got a hope of making a sub 500 micron adjustment. then you have to take in atmospheric conditions wow there goes your 45 micron again! I for one can sit there on a dead still night with a ED 80 on a EQ6 Pro mount and watch my FWHM jump from 2.3 to 1.6 and back up without touching the scope! If your using a really high end focuser aka Feather touch or even better with full robotic control, you would only be looking at 100 micron adjustments maybe a little less. but in the same case as i pointed out with my ED 80 setup your chasing seeing to a degree.

IMHO unless your talking about massive optics, super fast F ratios, and getting quality only seen in really high end optics/scopes your flogging the rotting carcass of the horse. sure make things as good as you can but save your sanity as there are alot of other things to worry about before you start worrying about a 45 micron shift in 800-1 meter of tubing!;)

Bassnut

10-12-2009, 12:44 PM

Thats a good point actually, and up to 8" of aluminium spacer tubes, mmmm.

bmitchell82

10-12-2009, 01:08 PM

for true zero shift telescope you need to get rid of alot of things!. Isolation is the name of the game.

CF in conjunction with Al make for a good combination. CF to join the secondary mirror to the top tube ring, CF for the scope tube to the bottom scope ring, CF to join the bottom scope ring to the primary mirror fixture. Good design will limit the use of tube spacers to get focus. aka design the scope for your end game! that is pick what equipment your going to use and measure it exactly. make the actual scope adjustable to within a poofteenth of where you need to be for focus. that way you can place your sensor in the Critical Focus Zone without having to use 15cm of spacers to get there.

GSO RC scopes are what i call top of the bottom of the range similar to a EQ6pro but they are limited to what they are doing because they need to appeal to the whole community (silly if they didn't) that is, people with DSLRS, DSI's, SBIG's, OSC, Mono, AO, OAGs.

Hence why they make it there setups the way they do so that joe blogs with what ever can make it work! sweet made a sale! and why RCOS and DS instruments and the like are so damn expensive, they go the extra mile, and a basic assumption that your using high end gear on the scope which slots you in a limited range but within saying that gives you Aston Martin proformance!

Head to the Deep sky instruments web page and all their astro photos taken are with Dedicated CCD's, not to discourage would be buyers, but if your coming to buy something like that your normally not about to buy your first scope!

I myself am trying to source some GSO 6" RC mirrors and will be designing a little travel/photography scope. the aim of that game will be as light as possible with quality setup so i can whip it in my suite case and have something to go with! I have access to machines that are accurate to .001 mm yes thats 1 micron but my tolorances will not need to be this tight. and i will assure you that im not worrying about a 20 degree temperature differential (unless im in the sahara desert) so alot of my equipment will be ally with a bit of CF for asthetics

Kal

10-12-2009, 01:30 PM

I am not missing any point. In fact, if you read my post, you will see quite clearly that you missed my point. Mirror spacing has a far greater effect on focus than the tiny focal length that an aluminium focuser has. The focal length of a focuser is maybe 100mm at most, so any contraction that it experiences through a change of temperature is very small. The change of separation between two mirrors in a telescope, however, can have a much larger effect. If the tube is X mm and you get an expansion/contraction that Alex calculated at 45 microns, it will equate to a change in focus at the focal plane of a much higher number. think of a SCT - if you add an external focuser your focus control is very slow compared to how much focus change you get from moving the primary mirror. I don't have the exact math, but a change of seperation of the two mirrors by 45 microns will certainly not equate to a change of 45 microns at the focal plane - because of the secondary magnification it will change the focus point by 5x this amount to 225 microns.

bmitchell82

10-12-2009, 01:42 PM

225 micron is still insignificant in the quality of our amature setups! and I didn't miss your point one bit. im just saying that your flogging a horse thats already dead because the average human hair on your head is 100 micron rip 2 hairs out sit them together and tell me your still serious that your going to be able to get that kind of accuracy in a mass produced product.
http://wiki.answers.com/Q/What_is_the_thickness_of_a_human_ha ir_in_microns
are you seriously telling me that your optical setup is going to be that exact? if it is then i stand aside as you have way more money than i will ever have.

and if i belive it to be correct that expansion is at a 20 odd degree differential. now normally youll get around 10 degrees which is half the 20 so lets half the 45 for a start to 22.5 and times that by your x5 112.5 micron!

It would be like me specifying in the engineering plans for house that all connections and interfaces must be within 1 mm... the contractor will laugh in your face followed by are you serious.!

bratislav

10-12-2009, 01:46 PM

More like 26x (secondary magnification squared, plus one). That is why SCTs have such a huge focusing range for relatively small movement of primary !

bratislav

10-12-2009, 01:50 PM

And if anyone missed that, let me rephrase.
Yes, for 45micron spacing change between primary and secondary in a typical SCT (5x secondary magnification) focus will move more than one millimeter !
Now you understand why they use carbon trusses in high end RC designs ... It is not for looks !

bmitchell82

10-12-2009, 01:55 PM

Thankyou for that Bratislav i am no expert in magnifications hence why i didn't factor that part in. Its great to have somebody with experience and knowledge in these matters weigh in.

It still comes back to my original statement that isolation is the only way you will get rid of the problem, isolation costs $$$ and alot of it for high end tolorances!

Kal

10-12-2009, 02:05 PM

Thanks mate. I knew the concept, I just didn't know the exact math of how to calculate it. :thumbsup:

Kal

10-12-2009, 08:13 PM

OK, I've decided to put the effort in and do the math open to the public so if I get it wrong feel free to correct me. I will have to make a few assumptions, since I don't know the full specifications of the GSO 10" RC

Calculating Expansion of the tube - which effects mirror seperation

Expansion = z * L * T

Where:
z = Coefficient of linear expansion of the material
L = Initial length (metres)
T = Temperature Change (celcius)

For aluminium, z = 0.0000231 per degree
I'll assume a tube length of 40cm (I don't have measurement)
I'll calculate for temperature change of 20 degrees

Therefore expansion (which is a contraction since the temperature change is a negative value) = .0001848 metres = approx 185 microns

Calculating focus shift

Focus shift at focal plane = -Am²/[1-A(m-1)B]

Where:
A = change in mirror separation
m = secondary magnification
B = secondary mirror to primary focus separation, negative in sign for a cassegrain telescope (the RC layout is a cassegrain configuration)

A will be 185 microns
m I will assume to be around 4 (the scope is F8, so maybe F2 primary and 4x magnification secondary?)
B I'll assume to be about the tube length I used earlier, 40cm.

Therefore focus shift works out as 0.002955 metres, or nearly 3mm for a 20 degree drop in temperature !

Bassnut

10-12-2009, 09:23 PM

So how much say does 150mm of aluminium spacers at prime on the above example make to focus shift with a 20deg drop in temp ?.

Assume the tube is CF and has no drift at all, ie what affect do the spacers have by themselves. I guess the formula is different as the mirror spacing is constant?.

AlexN

10-12-2009, 09:30 PM

~63 microns expansion for the tube in a 20 degree temp drop Fred..

Expansion is expansion, if your mirror spacing does not change, the only thing you have to calculate is how far the sensor is moving with regards to the focal plane in a given temperature drop.. 63 microns would be well within the CFZ of your scope, hence, as you mentioned earlier, you get 0 focus shift night after night with your scope...

Bassnut

10-12-2009, 09:38 PM

Thanks Alex. Then its interesting that RCOS include automatic focus temp compensation in the control system on the tube, makes me wonder why (mines not calibrated, so its not on, never needed it).

AlexN

10-12-2009, 10:03 PM

It snows in some places :) I dare say that, combined with wind chill factors would cause more serious expansion than what we commonly experience in Australia...

Its funny that you have TCF-S on your SCT, and TCC on your RCOS, yet in both cases have not calibrated either for temp compensation :D

My focus doesnt SEEM to shift much in my APO, however in my C11 it would shift almost hourly as the optics and internal tube temp started to equalise.. If I'd had the ability to have temp compensation, I would have!

gregbradley

10-12-2009, 10:36 PM

With the FSQ106 you need to refocus every 2 degrees C change in temp. That is F5.

With my other refractors I see focus shift when temp drops perhaps 4C but 2C is not that noticeable. These are F7 and F7.5

So I take it the faster the scope the more aluminium tube will cause focus differences.

The lens also changes focus with temp and this reduces the amount of focus change on some scopes per Roland Christen. He recommended refocusing with every 1C change in temp. That would be OK if you are using Focus Max or temp compensating Robofocus, FLI PDF and or using CCD commander to automate your runs.

Otherwise I can't see myself hanging around my scope all night in case the temp drops 1C to refocus.

The BRC250 has an aluminum tube but it has temp compensating rods I think in front of the corrector to move it when temp changes. It was not that sensitive to temp changes but still a bit.

CF seems the way to go for compound scopes but not APOs where
cooldown time is important. CF also has more tube currents I am told.
Hence another reason for the fans.

Greg.

AlexN

10-12-2009, 10:51 PM

Greg, Yeah I mentioned fast refractors earlier in the thread.. My TMB 80mm F/6 seems stable at prime, however insert the reducer and run it at F/4.8 and all of a sudden I get shift... I run a JMI motorfocus through a FCUSB controller for auto focus, and while its not temp compensating, I can script in focus confirmation through CCDAP.. There is no way I'd sit there watching a thermometer all night refocusing manually every hour or two...

The reason the faster scopes are more sensitive to thermal expansion is that the faster the optics, the slimmer the Critical Focus Zone.. at F/6 mine is 79 microns where as at F/4.8 its 50.6 microns... I'd hate to be trying to manually focus an F/2 camera lens with a CFZ of just 8 microns...

Hagar

10-12-2009, 11:14 PM

I have a robofocus unit fitted to my FSQ106Ed and use temp compensation. It is a requirement with this scope.
I also live in an area with probably the biggest shift in temprature or close enough in the country but while daytime tempratures can be as high as 25 during winter and overnight minimums down to -4 it has to be remembered that by the time I start imaging the temp has usually fallen to 0 degrees already so a variation of 4 or 5 degrees is not an awful lot. On most nights I only require 2 or 3 temprature compensation changes during an entire night. if I use the focal reducer I need a few more. f3.6 is just too fast.
The thing which must be remembered with these 10" scopes is that CF or aluminium tubes is probably of no concern. The mirror cell and the front of the tube are connected with huge slabs of Aluminium top and bottom. In reality you are probably better of with the Al tube as there will be less wear and tear on the aluminium to aluminium surfaces with equal expansion coeficients than Al to CF with difering coeficients. Focus changes can be compensated for with hardware and software but wear and tear cannot.

gregbradley

11-12-2009, 07:30 AM

Interesting. So that's why.

CCDAP which program is that? I have to get my temp compensating robofocus callibrated. You have a routine to go through to set it up.

Greg.

rat156

11-12-2009, 08:09 AM

C'mon Doug, I hardly think it shifting 185 microns is going to amount to a lot of wear and tear!

CF is the way to go for these tubes. It's light but strong. I'm sure someone can engineer the mounts for the dovetails so that one has slip in one direction but it's firmly held perpendicular to that direction.

I understand that it will cost more, everywhere else in the world Aluminium is cheap, not in Aus though, so if you price Al tube locally it would be much of a muchness. This probably shows that the Chinese CF industry is not up the the standard of the developed world. I have Kevlar parts made for cars, hand made by a guy here, who charges less than $500 each for them.

If you can get me the dimensions of the tube I can ask him to make some if anyone is interested.

Cheers
Stuart

Kal

11-12-2009, 09:00 AM

I'd have to agree with Stuart. If there was wear and tear people would be noticing it on the 8" RC's, and I haven't heard of any issues with it.

Hagar

11-12-2009, 09:31 AM

I understand 185 microns isn't a lot of movement but it still is a movement which isn't required. It is a bit like a corrugated iron roof. Screwed down to a hardwood frame the iron creaks and groans with temprature change. It is infact enlarging the holes the screws go through. I know this analogy is a lot more violent than the 185um talked about here but rgardless there will be some movement in areas the CF is used to prevent such movement.

It is possible to engineer a mount base which has no connection between the front and back of the scope, in fact RCOS provide this.

I actually own an 8"RC GSO and will watch for damage caused by expansion but doubt I will see much over this short length. It is getting plenty of time to stretch and shrink while waiting for the clouds to clear anyway. I have just fitted a robofocus motor to it and will be interested to see what if any movement there is with temprature shift.

The comments I made were purely based on engineering principles and I still stand by them as true. In the real world the mirrors and focuser etc will probably be totally stuffed by the time this wear and tear is evident anyway. It was purely an educated, informed statement of fact. My degrees allow me to make them.:shrug:

Bassnut

11-12-2009, 11:08 AM

Well, the proceedure is not that clear and quite convoluted for the TCS-F, I think calibration requires constant refocusing during a sizable temp drop time period of maybe an hr or 2, and then all over again if anything is changed in the imaging chain. I always thought stuff it, ive wasted 2 hrs if it doesnt work, and multiple tries before I understand the instructions, id rather image now thank you, maybe tomorrow :rolleyes:.

netwolf

11-12-2009, 06:27 PM

An interesting add here on amart, a US company custom making a CF tube for a C14 for ~500USD

http://www.astromart.com/classifieds/details.asp?classified_id=660192

A bit more digging and found this site for selling the above and other CF OTA tubes. Looks like its a work in progress ad links dont work.
http://carbonscopetubes.com/

This is the companies normal website for hobby rocket frames
http://publicmissiles.com/

AlexN

11-12-2009, 06:32 PM

Fahim, There are a few companies in the USA making CF tubes for the Celestron SCT's.. I was looking into getting one for my C11 back in the day.. It was $380USD or there abouts, plus about $130USD shipping... :eek:

netwolf

11-12-2009, 08:45 PM

Alex one would think the C11 OTA might be in the same range as the GSO 10" RC so 1000$ seems quiet unresonably high.

AlexN

11-12-2009, 09:28 PM

I'd agree Fahim.. I wouldn't pay $1000 extra for the CF tube on the GSO 10" RC. I'd pay ~$700 for robofocus.... Temp compensation, automated focus routine, and $300 cheaper.. you end up with 0 focus shift (better than the CF tube, as the Aluminium parts will still shift. Temp Compensating focusers negate any and all focus drift due to temperature...

I think if anyone was considering the 10" RC, get the Al tube model... I would love one.. I don't have the mount for it though..

marki

11-12-2009, 09:56 PM

Alex you probably need to factor in the time it will take you to get the temp compensation working properly (right pain) and also that any changes to the imaging line will require you to do it all over again. What is your hourly rate coz you need to factor that in as well :P. I have a temp compensation system on my LX200 and everytime I get close to getting it right I go and buy something else to stuff it up.

Mark

AlexN

11-12-2009, 10:20 PM

Yeah this is true.. but even if you get the CF tube model, the mirror cells are aluminium, and will expand and contract. the focuser and extension tubes are aluminium, and will expand... So pay $1000 and still have to fix the focus when the focuser and extensions expand, or spend 700 and a night calibrating a temp compensated focuser....

Oh, better yet, dont calibrate the temp compensating focuser, Just automate your imaging run using CCD Commander / CCD Auto Pilot etc and have it check focus periodically during the imaging run, and adjust if required... There you go, 0 time spent calibrating it, reliable good focus, and $1000 cheaper on the OTA.

This could be done using something a lot less sophisticated than Robofocus. I have a JMI Motor focuser on my TMB using a shoestring FCUSB controller... we're talking $300 all up, and I do not touch the focuser at all... despite it adjusting and compensating for temperature changes during the imaging run..

Hagar

11-12-2009, 11:17 PM

I have temp compensation on both scopes fitted with robo focus and it is a real pain to get the focus slope set correctly and the temp sensor is not on the focuser but mounted in the bottom of the control box. It is a lot easier to run focus max at the start of your imaging, get a couple of good V curves and use it during your session. It seems a lot more accurate and an auto focus takes about 28 seconds using Maxim and focus max with robofocus. I think I would also stick with the Al tube as the CF in this case is expensive and somewhat of a gimmick. Looks good but serves no real purpose.
Please don't argue about this statement, just my thoughts and what I would do. By the way Robofocus is only $500 at the moment and a second motor is about $132.

AlexN

12-12-2009, 12:13 AM

Robofocus is only $500!! :eyepop: !! Bargain..

I agree completely Doug, if robofocus is that cheap, FocusMAX is free, there is the simplest solution to beating any focus drift.... You most definitely understand the need too.. From what I've read, the FSQ106 with the reducer is a focus shift nightmare... I'm kind of happy I went for the TMB 80/480 in that respect... Sure the field is not flat like an FSQ, but its minus that major pain in the backside...

Hagar

12-12-2009, 08:10 AM

It does appear a pain but with focusmax and robofocus the job is a real easy task. Pause image collection push one button an hey presto perfect focus. Resume imaging. Temp changes mor than 1 degree benifit from a focus reset.

The FSQ does drift quite abit with focus but to be honest the scope really performs at it's best at F5, 530mm witha huge image circle, no vignetting and a flat at field. I love it.

Mighty_oz

12-12-2009, 02:36 PM

Q for u all how do u think this RC will compare to say a C11 optic wise for imaging with current knowledge ?

AlexN

12-12-2009, 02:53 PM

Going purely on the quality of the optics in the 8" RC, I would say that the RC was better for deep sky imaging than the C11.. The RC is also faster at F/8, this is a plus and a minus really... it shortens your focal length a bit, but the advantage is that you're sucking photons in at F/8 rather than F/10.. The C11 is fairly heavy, I would not be surprised if the 10" RC comes in a little lighter. If buying new for new, the C11 OTA will cost you more too...

In either case, I would say minimum spend on a mount for either of these scopes with deep sky imaging on the agenda would be around the $3500 mark.. I would't mount either scope on less than a Losmandy G11 with the intention of deep sky imaging... An EQ6 Pro will hold both, but the whether or not you get the results you're hoping for will depend greatly on too many things... The EQ6 would be fine if you had adaptive optics for instance...

Optically, If I was buying a new scope tomorrow, the 10" RC would be chosen over a C11..