Calibration frames

[E_ri_k]

I was going to do a set of around 100 Bias frames and combine them to a master. I thought all the frames should be pretty similar, but after the 5th shot I take there is quite a big difference. Is this normal?

Camera is a QHY10 with the temp set to -20.
Erik

[whzzz28]

When are you taking these shots?
If your taking them whilst inside, make sure the cap/whatever is over the end of the lens properly and use some alfoil to cover the noise point.

That being said, this could be heat related.
Set a delay between shots of say 10sec and start again. Does it still build up over time?

Also, make sure you keep an eye on your histogram sliders in Maxim, in case the sliders are moving for some reason (do you have it set to auto? try manual if so).
Open up say the 110 BIAS file and make sure the sliders take the full histogram into account. Cut off part of it and you will get images that look like this on your screen, but the actual data is fine.

[E_ri_k]

I took them about an hour ago, camera attached to the scope with the cover on, in my OBS, pitch black. It can't be light. I had a look at the histograms. In the "good images" pixel values ranged from 350-450, and the bad ones around 600-900. Had it set to "Medium" It's funny though, did a set of 32, the first 5 were good, then all bad. Did another 32, and the first 25 were good, another 32, and they were ALL good. So I kept going for another 15 or so, to make it to 100, and it has seamed to work... Don't think it built up, it was a bit random.

I had a look at the FITS header for both images, and the temperature was round about where it was set to (another annoying issue is the temperature wont stabilise) but anyway...I got my 100 files, so that's a start I guess.

Erik

[multiweb]

That's an odd one but to me it looks like a TEC issue. I had the same problem on the 8 at one stage with one bad power connector. The pattern is a dead give a way. Have a talk to Theo (Gama).

[pmrid]

Nathan, you might want to think about the possibility of stray light in the obs. For example, if you look at the focuser drawtube - there is a gap between the tube and the focuser body - so someone sitting with a headlamp on reading his collection of Batman comics while the scope takes calibration shots could well be shining right up the side of the focuser tube. I've done it myself. Or it could be an overbright LED on some piece of equipment. Have a critical look at all lights in the obs - however small. And tape over any that are more cosmetic than functional.

Peter

[Shiraz]

ditto with my 8 - similar pattern. bias-0011 looks pretty noisy as well.

[multiweb]

That's just the way it's stretched on screen I think. No to worry.