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A couple of initial thoughts:
If you're using a ToUcam (which a 900nc is) 15fps is causing compression. Try backing it off to 5 or 10fps.
Also, onion rings are most often the result of underexposure.
What capture software are you using? Make sure you've got a full histogram. If you're not using capture software which gives you a histogram reading or light meter reading pre-capture, download one. I use K3CCDTools...but others are also good.
It's most likely the image looks 'scratchy' because you're having to push the gain, as a result of your settings and the fact you're using a 5x powermate which isn't giving you enough light due to the focal length.
Try 10fps...
A 5x powermate is a fair amount of additional focal length for an 8" instrument.
The seeing would need to be very good to stand that, and it ain't been that good in Bris of late.
Last edited by matt; 18-07-2008 at 09:57 PM.
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