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Old Oct 31, 2005, 7:02 PM   #1
Join Date: Nov 2004
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I have a Celestron C-90 telescope that I was thinking of using as a telephoto lens on my 20D. I know it will be manual focus. Does anyone have any experience with this combo? Image quality? effective focal length? sample pictures?


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Old Nov 5, 2005, 9:38 AM   #2
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Image quality: GREAT

Effective Focal Length: If you are using it for prime focal, the C90 is like just another photo lens for your 20D with focal length of 1200mm (x1.6 = 1920mm with crop factor). In this case most likely you only need a EOS->T2 adapter / thread converting ring to connect the camera and lens up, manual focus with the focusser of C90.

If you would like to mount as afocal it is not impossible but it would be much more complicated and some more tailor-made adapters might be needed as well.I did not try that way so leave it to professionals.

EOS->T2 adapter is something like this: (disclaimer: seller isn't me :-))


The manual of C90 might be helpful? T adapter is exactly the T2 thread:




(PS. One pre-caution I learned last time I mount my scope on 300D is, be sure to clean / blow away dust from inside your scope as good as possible before you mount them together to avoid excessive dust flowing to the CMOS sensor)

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