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Old 27-01-2014, 06:10 PM
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RickS (Rick)
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Originally Posted by gregbradley View Post
I got a reply from Richard Crisp. He said that doing 20 darks would reduce noise more than averaging the overscan area as its only a narrow

I get from this there is a benefit from doing overscan callibration if your camera has a bias drift.

He recommended measuring it. So I will do a test and see how much the bias shifts over say 20 bias's at different times at the same temp.

Hi Greg,

I have significant bias drift on both my KAF based cameras (SX H-18 and Apogee U16M) which is why I started digging into this in the first place. I agree YMMV depending on your camera/sensor and if your bias is stable then it is better not to do it.

In my case I found that overscan calibration made my master darks look much more linear (as did Dave) and the final integrations showed measurably better SNR.

From memory, the bias drift on the U16M was as much as 40 e- over a few nights. That's an order of magnitude more than the signal I've managed to tease out of a couple of targets. The jets of NGC 1097 are a good example. I don't think I could have picked up R4 without overscan calibration.

I'd be interested to hear how your cameras measure up.

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