[gregbradley]

Originally Posted by PRejto

Hi Greg,

This is what Stan wrote:

"Sony CCDs have remarkably uniform dark current (pixel-to-pixel) and often do not need dark subtraction. In fact, dark subtraction may inject more noise than it cures (that's why it is advisable to use a very high quality dark). But when avoiding dark subtraction, it is necessary to remove the bias or bias level (pedestal) in order for flat fielding to work properly. And it might be useful to mask out a few consistently bad pixels. This can be implemented in CCDStack."

So, I don't think he is talking about the choice of bias subtraction whilst making a dark vs. doing the bias subtraction when running the calibration tool. I think he is speaking about actually using a dark (or a bias frame as a dark).

Yes, you can make a pixel map and map the columns. You just use different rejection tools. There are examples of doing it free hand in Adam Block's tutorial.

Peter

Thanks Peter. That's good data. Is this on the support forum for CCDWare?

Originally Posted by RickS

Greg,

My experience is that rotation of the whole camera/FW/OAG assembly doesn't affect flats on the systems I use. However, this would not be the case on a scope where the rest of the optical system introduced some vignetting, especially if the camera isn't perfectly centred. I guess it's something you need to test. The old calibrate a flat with a flat trick would come in handy...

Cheers,
Rick.

Testing is good to know for sure. Not sure what the calibrate a flat with a flat test is. They null each other out?

Greg.