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astrosathya

Pixel resolution and choosing a CCD

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I am deciding to jump in and purchase a used CCD camera. Some of you may already know of my plans as I have posted them on other popular fora a week back.

I am in a dilema because one question plagues my mind. The Orion G3, being a started CCD is also easy on my pocket, specially a used one. The upside with it is that it is a perfect match for the GSO6" RC that I am buying this month (gives me 1.31"/pixel). However, it has a pixel array of ~ 750x520 which means that the full size image will still be quite small. Other than the small array, the chip does have some good characteristics like 50k full well capacity, low noise etc. Which other camera would match up to it and why? Any experiences anyone?

Edited by astrosathya

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Before going down the slippery path of AP read either or both of these books.

Make Every Photon Count and Astrophotography by Thierry Legault, both are excellent and offer clear explanations.

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My personal opinion is that matching pixel size to focal length has a great deal of uncertainty to it. So there is no "perfect" match.

The traditional view is that since atmospheric turbulence affects the ultimate resolution that a camera can achieve, there is little point in using a camera / telescope combination that gives higher resolution.

That is clearly correct in theory. However, in practice "seeing" is never a constant and can vary by up to a factor of 10, both between users' sites and on different days. We also know that individuals can produce very good images even when their setup is far from the optimal values.

So I wouldn't put too much importance on getting a precise match. It's also important to remember that you can put focal reducers / correctors in front of the CCD to change the focal length and therefore the arc-seconds per pixel resolution (and field of view). With small chips there is greater scope (sorry!) for higher focal reductions without affecting the image that hits the CCD.

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Before going down the slippery path of AP read either or both of these books.

Make Every Photon Count and Astrophotography by Thierry Legault, both are excellent and offer clear explanations.

Thanks for that. These books are not available in India and very difficult to get hold of them. Also, I've been doing AP since 2006 starting with a film camera and DIY barn door. I also worked at Opticstar Ltd, Manchester till Oct 2012 :p and now my first book on AP is in the pagination process, will be released early next year. I do however look forward to reading any good book on AP I can get my hands on.

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If you're writing a book on this stuff, isn't this basics that you should know about already? .... sorry just asking :)

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The OP is just asking for thoughts from people with experience on alternative cams, he didn't ask about any technical stuff :smiley:

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The G3 is a decent starter CCD. For the price its is hard to beat. You just need to ask yourself if you can live with its aspects that arent that great. Though it has cooling it is only -10C ambient, which is much but better than none. So on hot summer nights you might not get as much relief from only the -10C. The next thing is the very small FoV. Especially when combined with that RC. At F/9 you will fine the FoV very restricting. Examples here. Those two examples show a very small field and they where taken with a 8" Newt that has a much short FL than the RC. Now they are cropped but you can see full res on his astrobin link in the article. Even with a reducer on the RC I still think you will find most of the larger object wont fit on your sensor. Now some people don't mind that at all and if thats you then you'll be just peachy. But just wanted to point it out. If you have stellarium you can enter the scope and camera into the program and it will show you the FoV that you will be imaging with. Then you can look at different targets and see how much or how little room you will have. Best of luck to you....hope you dont get bitten too hard by the AP bug ;)

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Even though he only asked for thoughts from those with experience of alternative cams? I don't think anyone can be expected to know about all available cams !!

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Sara Wager is well known even down here for her exceptional work. So no, I did not take any offense. But yes, as Freddie said, the technical stuff I am good with, its just that I am a little fickle minded when trying to choose a camera. That is much more simpler than everything else. Yes, In my book I have given "just enough" coverage for the nitty gritties of choosing a DSLR or a CCD, but not too much that it will put off the beginner as he/she may get intimidated by all the tech talk. 

The Gentleman from USA is almost reading my mind. I like the G3, and I've plugged in its specs into CCD Calculator too to check the FoV. For large objects I have my 80ED+Canon500D combo which again is an ideal theoretical combination giving me 1.51"/pixel. The G3 will be mostly used with my 6" RC which is somewhere in the sea between Taiwan and Mumbai. :)

So, Olly and Sara, Thank to you both, a lot of us down here do stay inspired because of your work, I am but a beginner in this field. I have interacted with Sara on Disciples of the Dark Arts too. I think we need Olly on that forum too.

Edited by astrosathya

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For what it's worth, I used to have a G3 and found the software that comes with it to be a complete nightmare. I never got it to perform very well and sold it on.

Peter

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