Magnitude limit capability of webcam system

[tonyowen]

I have a 75mm obj, 1220fl telescope, a (unmodified) spc880nc webcam and a 2x barlow; all running on a Vista based laptop

Even with exposure, gain and brightness set to their maxima I cannot view relatively dim objects such as Saturn (low in the SE) using the webcam and 2x barlow combination.

The webcam and barlow combination presently allow viewing and capture of Jupiter (just) and Venus.

How do I calculate the expected limits of capture in terms of an object's magnitude; and what 'seeing conditions' does any such calculation assume?

regards

Tony

[tonyowen]

Does nobody out there have any thoughts, opinions, experiences, or comments?

regards

Tony

[Cornelius Varley]

I don't think there is an easy answer. I think trying to image at f32.5 with a 75mm refractor is beyond the capabilies of the telescope.

Peter

[JamesF]

I'm in agreement. I just don't think you have enough aperture to image Saturn at that kind of focal length with the short exposures you're going to get from a webcam. It's just not bright enough. I'm finding it tricky enough with a 127mm scope at the moment.

I'd not be surprised if there's some way to relate focal length, aperture and time to achieve a minimum SNR on the sensor, but I've no idea how.

James

[cgarry]

I would have thought that focal ratio was all that mattered, not focal length nor aperture individually. The brightness of Saturn on a web cam at f/32.5 would be the same in a 75mm scope as a 14" scope, it would just be a much smaller image with the 75mm scope.

Having said that, I think f/32.5 (and probably larger depending on the spacing) probably does produce an image that is too dim for the webcam to image without using quite long exposure times.

Cheers,

Chris

[tonyowen]

Thanks to all for responses

They confirm my empirical frustrations and results

regards

Tony