QHY8L artifacts with bright stars

[redfox1971]

Many of the images i have been taking lately have a bright star in the frame and as you can see from this one of m51 just stretched in pixinsight shows the problem i am getting,what could be the cause of this? when i look at the single frames i can not see this defect that runs to the right of the stars,so maybe the stacking in pixinsight is causing this,i use winsorized clipping.Have i maybe got the gain and offset set wrong.

[Oddsocks]

Since the black line is very faint I doubt you would see it in single subs, and PI, when stacking has revealed it.

I suspect it is a camera timing/gain adjustment that has drifted and requires readjustment, similar to the recent series of posts showing an identical defect, but much more severe, with a QHY9 camera.

http://stargazerslounge.com/topic/234078-qhy9-mono-camera-horizontal-black-lines/

If you want confirmation that it is a camera defect rather than processing you could post the same series of subs used to generate the picture above in your dropbox, post the link here and ask if another SGL user will stack and process them for you in PI, Maxim DL etc, or you could download Deep Sky Stacker and try a stack in that to see if the defect is still apparent?

https://www.dropbox.com

http://deepskystacker.free.fr/english/index.html

William

[redfox1971]

Thanks for the suggestions Oddsocks  i seem to have the same effect with deepsky stacker,I have just set my gain and offset once again and now have a gain of 6 and offset of 112,before gain was 6 and offset was 110 so not a lot of difference,will try again on next clear night.

[Oddsocks]

On the QHY9 I think it was an internal voltage/gain adjustment on the camera PCB, controlling the amplitude of timing pulses, that needed tweaking to remove the horizontal black lines rather than external software adjustment.

[ollypenrice]

This is surely a gain/potentiometer issue. I've seen it affect several SX cameras here while shooting in Bin 2. After email exchanges with SX and attempts to reduce the gain via the potentiometer we ended up giving in and accepting that the SXVH36 wasn't going to work in Bin 2, which was a bit of a blow for shooting at 2.4 metres of FL. The same thing affected a couple of their 8300 cameras seen here as well.

So I'm sure that's what it is, the artefacts being nearly identical, but what you do about it I don't know. There must be a way to turn down the gain.

Olly