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Should age matter on OTA's


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Hi Fellow Stargazers,

I am after some advice please or at least your thoughts.

An opportunity has arisen to purchase a second hand Celestron C11 XLT SCT OTA carbon fibre for the cost of a little over half price of a brand new one of nowaday.

History is, it was bought in 2006, has only cosmetic damage and slight correcter lens marks from cleaning which is claimed to not affect the optics in any way. Other than this it is in good working order. Also it is a USA edition not China made which I'm told is better quality.

My query (or concern) is should I worry over the quality of the optics and the XLT coatings as this is 7 years old or am I being concerned over nothing, also is there any truth in quality of where this was made.

I would love to go with the AP of the C11 but the age of it puts me off or should I go for a second hand C9.25 XLT OTA for a couple of hundred pounds cheaper?

You thoughts would be very much appreciated and thank you all in advance,

Richard.

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An older C11 should work very well..

With refractors some of the newer coatings are much better that the old ones originally used....having said that the best telescope I have is a thirty year old 4" Televue Genesis which is still going strong.

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Someone may well correct me on this, but I heard that Celestron still manufacture all the C11 and C14 OTAs in the US (only the C8 and C9.25 have gone to China).

That being said, Celestron really got good at producing their scopes a few years ago, with great consistency.

I own an older Nexstar 11GPS with carbon fibre tube that I bought in 2002 and now at over a decade old it still performs like it is new. The formula for the XLT coatings has not changed, and they are pretty durable, so as long as you can be sure the owner has looked after it well, you probably have a good scope on offer.

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Thank you for your responses, they are very encouraging.

I wanted to be sure as the idea of buying this is to last me close to the duration of my interest in astronomy (for life thereabouts)

My aim is to get into DSO astrophotography as well as planets and needed something that can see out there with ease hence my thinking of the largest AP I can afford.

I forgot to mention, the C9.25 is in mint condition and also from/made in the USA (not sure on it's age though).

Portability is not too much of an issue and I am hoping to attach to a CG-5 GT GOTO mount hoping it will comfortably handle the weight of the C11 with a DSLR attached without causing a strain on the gearing when slewing to track objects.

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I don't know the working capacity of the CG-5 GT.....

I had a C9.25 mounted on the HEQ5pro for spectroscopy a while before moving it to the NEQ6pro (better stability and control)...this was upgraded to the C11.

IMHO the C11 with all the usual "dangle dollys" is getting close to the limits of the NEQ6pro.

The C9.25 weighs 10.1Kg ( with dovetail) and the C11 12.5Kg (bare)

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Just looking at the specs on the flo website a c11 is approx. 12 kg and the cg-5 GT is rated at 7kg for ap. add a camera, guide scope etc you'll be at nearly double the recommended limit of the mount. of course thats a new c11, I don't know how heavy an older one would be

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If you want to do DSO AP then probably you still want to think through a few things to be sure you buy the right thing. How bright your images will look depends not on the aperture but the focal ratio. For AP the aperture only really influences the resolution, which likely tops out around 8" due to seeing limitations. The C11 is a slow scope, so you'll be needing longer exposures. Even the C9 is on the long side. The focal length determines the magnification and therefore the area of sky visible. Since these SCTs are rather long focal length they magnify quite a lot. Thus, you need accurate tracking and good mount to get this scope to perform well for imaging. This, coupled with the requirement for longer exposures, makes learning DSO AP hard with a larger SCT. Also, the larger targets won't be readily accessible to you because of the longer focal length. For these reasons, most people start off with a short refractor (even an 80 mm is great). Lest you think such an instrument will produce inferior images, take a look at this shot from a member's site taken with small scope: http://www.sunstarfrance.com/gallery_orig/images_lg/maurice-Toet.jpg

You can do DSO AP with an SCT. But when I see the old hands imaging, they're usually using refractors. The SCT will be fine for imaging the moon and planets, as you want the magnification for those.

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Umadog has it exactly right there :). You can do DSO AP with a SCT, but it's making more work for yourself (the exposure times with an SCT are much longer too).

The age of coatings shouldn't matter if it's an SCT, although mirror coatings for Newtonians often seem to need redoing if older than about 7 or 10 years.

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I must have mis-calculated something, had not realised the CG-5 GT had quite a low weight capacity, I can see FLO sells these C11's with the CG-5 GT goto mount, have I missed something here?

I would contact FLO about that. It might be able to work with enough counterweights (FLO have the C11 pictured with 6), but might be pushing it a bit. It does state 7kg payload for imaging and 10kg for visual in the specifications though ;).

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Umadog is right on the money. I wouldn't consider an 11 inch (or even a 9.25 inch) on anything less than an NEQ6. In all honesty I wouldn't even consider that, really, because although it is certainly possible to get the guiding to work for those focal lengths it is, in and of itself, a major undertaking to do so. And that's before you get anywhere near to taking a picture. I do use a large catadiotric for DS imaging. It's not mine and it rides on a premium Mesu200 mount which can handle the focal length (this is NOT all about weight) very comfortably. I would also say that even with the focal reducer/flattener you will only get the inner part of your image sharp with a pre-Edge SCT. A shorter focal length scope with better optics will probably do as well or better for AP. Visually the standard SCTs are good but AP is a special case.

DSLRs need fast F ratios to perform well because they are noisy and uncooled. Their large formats need a wide flat field. You'll get all this in a smaller refractor. This was done in 85 and 106mm refractors.

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-FGgG233/0/X3/M31%20LES%20OLLY%20TOM%20TEC%20CORE-X3.jpg

To answer your original question, I have a mid nineties Meade SCT which seems to perform as it did when new. I'd just want to know a bit more about those marks on the corrector though. If they are scratches they could matter a lot. But seven years is nothing if a scope has been kept safe and dry. And like Ken I have fond memories of my recently sold Pearl River Genesis. Good as new in its thirties!

Olly

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No problem. I think what you'll find with AP is that, if you get into it, you will need more than one scope to handle the full range of targets. A popular combo is something like a 3" or 4" frac and a fast 8" imaging Newt. But of course SCTs can play a role too for more specialised tasks. So a beginner may as well start with the smaller frac because it's way, way, cheaper to buy and mount. Test the waters with that and see how you are in a year or two.

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I have contacted FLO regarding the weight issue/question, so am awaiting a reply about that one, I am thinking I will stick with the CG5-GT mount but possibly now go for the c9.25 as this seems to be a good intermediate (not too small, not too large/heavy).

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Guys, you have all been a blessing with your wealth of knowledge in this and am now in re-think mode, my budget may need to be raised and which would then put me in the range of an EDGE HD 800 OTA which is now starting to sound like a good choice to last me a very very long time.

Umadog, I hear you about starting low then building up as needs required, my thinking is I know I am in this for the rest of my life as a hobby and money is tight so, while I have it now (the money that is) I want to buy a scope and mount that I would be happy with for a very long time if not forever more.

Cheers Rich.

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I understand where you're coming from :) Over the last couple of years I too have done all of my astro purchasing and am now laying off it. If you're doing the purchasing now, perhaps you should consider also purchasing a little refractor to go alongside the SCT? Not only can you do standalone AP with it, which is great for starting out, but it'll also make a good guidescope for the SCT. If you plan on serious AP with the SCT then you'll need a guider of some sort, anyway. It could be off-axis guiding but you'll get more flexibility with a separate scope.

Here's some info on the topic: http://homepage.isomedia.com/~cvedeler/scope/guide.HTM and here: http://www.sctscopes.net/Photo_Basics/Accessories/Guiding_an_SCT/guiding_an_sct.html

Orion do a nice 80 mm for under 200 dollars (so with luck under 150 GBP). There's a review here: http://www.islandnet.com/~cspratt/short.htm and you can see the product page here: http://www.telescope.com/Telescopes/Refractor-Telescopes/Refractor-Optical-Tube-Assemblies/Orion-ShortTube-80-T-Refractor-Telescope/pc/1/c/10/sc/346/p/9946.uts

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Umadog, thanks again for some sound advice and for the links too, I certainly need to go and do some more homework etc.

As for everyone else, thank you all as well as all information in this thread has been taken on board and will help me to decide what I actually need.

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