Canon xTi and Celestron C-90 (1 Viewer)

I have an older C-90 that I bought years ago, and used with a 35mm manual camera. I now have a Canon xTi and bought a T-ring adapter to use with the C-90. The scope is rated 1000mm f/11. While I still am having some issues with focus (but getting better), my main issue is when I look at aperture on the camera it displays "0", and I can't adjust it, thus my pictures tend to be quite dark unless it's a bright day. The hookup is camera, T-ring, scope just as though it were a regular lens. Any thoughts around this?

Bill

The diameter of the scope is the aperture and that is a fixed size which is why the camera can't control it. The only way to get faster speeds is to get a decent focal reducer which will reduce the magnification of the scope and thus increase shutter speed. Also set the camera to around ISO800 which will also increase the shutter speed. Make sure you are using the camera in manual mode and adjust the shutter speed manually to give you the correct exposure.

Paul.

Paul Corfield said:

The diameter of the scope is the aperture and that is a fixed size which is why the camera can't control it. The only way to get faster speeds is to get a decent focal reducer which will reduce the magnification of the scope and thus increase shutter speed. Also set the camera to around ISO800 which will also increase the shutter speed. Make sure you are using the camera in manual mode and adjust the shutter speed manually to give you the correct exposure.

Paul.

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Thanks for the information Paul. That makes sense to me, so I will give it a go next time.

Cheers,

Bill

I use a 7D on my scope with a non-standard lens adapter which also shows "0" as the aperture setting. Setting the Mode Dial to AV allows the camera to set the correct shutter speed automatically. Paul's suggestion of using a high ISO will help combat any camera shake or vibration.

Mike

Thanks Mike. I will certainly try out these suggestions come springtime. I will be heading to a bird festival in Maryland in mid March, where there are a lot of raptors and other birds nesting. I plan on taking the Celestron with me and hope to get to some great pictures with it.

Bill