davidmalanick

On 06/01/2022 at 15:17, vlaiv said:

In order to figure out best offset setting for given gain - you only need bias exposures.

Procedure is rather simple:

1. set some offset

2. shoot a number of bias subs with camera (say 16)

3. stack those subs using minimum method

4. examine statistics of resulting stack. If minimum pixel value is larger than 0 (or whatever minimum value for camera is) - you are done, if not, raise offset and go to step 1.

Visually, histogram can be "glued" to left side - but that is just visual thing, you really need statistics in order to know values. If you have 0-65555 levels in pixel value and histogram on screen is say 300-400px wide, how can you tell if histogram is at pixel value 56 or 72 or is at 0? Visual histogram does not have enough resolution to provide feedback for that.

Btw, setting offset a bit "too high" is really not a big deal - it won't affect your image at all in the end. It will reduce your full well capacity a bit - but that is not big deal, you'll need to take short exposures anyway if you want to capture star cores that are usually blown in regular exposures.

This seems like the easiest method of computing offset I have ever seen. Could you please go into more detail on program usage?  I assume you are using Pixinsight. That is what I used for step 3. My question is on #4, where do you find minimum pixel value?  What process, what field is it?

Thanks!