CMOS Image Capture Problem

[groberts]

I've been using a ZWO ASI1600MM-Cool camera + ZWO filters with Astro Photography Tool (APT) successfully for some years but recently, usually when capturing Luminance, the resulting sub seems to be blown out as if overexposed.; APT shows each sub as very bright if not completely blown out.

I've played with the histogram settings without success and when I look at the subs in more detail in PixInsight it's clear that the basic raw sub data is heavily shifted to the right. Manual stretching after stacking sorts out the problem, by moving the black and mid-tones to the right to obtain a 'normal' stretch but I'm wondering if there's something I've got wrong in the capture set-up?

I should point out this does not usually happen with other filters, especially narrowband.

Attached is a basic 180 sec L sub straight out of the camera showing the skew to the right - even before manually correcting this once stacked the subs look a bit better in PixInsight.

Graham

[The Lazy Astronomer]

Any change to the capture software or camera driver? If not then maybe gain or offset has been changed accidentally? 

[groberts]

2 minutes ago, The Lazy Astronomer said:

Any change to the capture software or camera driver? If not then maybe gain or offset has been changed accidentally? 

No same as usual + including the gain and offset which is shown in the attached FITS header.

Graham

[tomato]

I don’t know if you are out with your set up when imaging but maybe the local light conditions have changed, eg a neighbour has installed additional outside lighting?

[teoria_del_big_bang]

I must admit if that image preview is unstretched the background looks very bright what is the scaled value if you hold the curser over background in PI ?
It does look like there is a lot of light polution about.
Are your RGB images okay , I know you say they are but  the same but I expect they would not suffer as much as the lum and possibly the NB would hardly be affected.

I now its not comparing like for like as I have different scope but heres one of my Lum images form a few years ago with same camera but different scope.

Not sure this helps at all though 😞 

Background measures an average of about 0.12 in PI but this was a 600S exposure so with similar skies 180S shoud be much les than this.

Steve

[groberts]

Thanks for the comments so far.

Steve - the background measure for an L sub is 65 but given the right skew of data originally posted above this is to be expected, though it is obviouslly not correct;  R = 16 and Ha = 0.014.  After applying a basic Histogram Transformation to the L sub the value is 16, with normal data distribution now shifted towards the y-axis.

There has been some increased light pollution this year from new neighbours but I now use a screen to shield the scope + when they've gone to bed and the lights are out it's fully dark but the problem still persists i.e. has to be a settings problem?

Graham 

[teoria_del_big_bang]

Strange, have you taken any darks or bias frames since the probem happened to see if they come out as normal ?
Just thinking if they have changed it does eliminate the LP possibility and does put the issue with the camera whether settings or something else.

Steve

[groberts]

24 minutes ago, teoria_del_big_bang said:

Strange, have you taken any darks or bias frames since the probem happened to see if they come out as normal ?
Just thinking if they have changed it does eliminate the LP possibility and does put the issue with the camera whether settings or something else.

Steve

No recent calibration frames as I'm working from a library, though it's an interesting thought and will give it a try when I'm next set-up.

However, I image with a William Optics GT81 + ASO294MM Pro camera as well, also using APT image capture and have no problems, as you can see from this recent L sub below, with the data distribution nicely bunched towards the y-axis.  Which, I think rules out LP? 

Graham

   

Edited October 20, 2023 by groberts

[teoria_del_big_bang]

6 hours ago, groberts said:

Which, I think rules out LP?

Yes Graham certainly seems to be pertaining to the camera whether settings or a fault (which I hope it is not).
I just can't think what settings could be wrong all in the fits header looked fine. What if you try using the camera in the software supplied by ZWO just to try a capture, clutching at staws a bit but using the cameras supplied capture software is where I tend to start with diagnosing these sort of issues.

Steve

[groberts]

Hi Steve + thanks for all your comments.  I've used this camera + ZWO EFW and filters with APT since 2017, first with the WO GT81 and then now with the Samyang 135 on the same laptop all the time, which has been faultess so far.  Will take a deeper look at settings + software but nothing obvious springs to mind, unfortunately.

Graham

[teoria_del_big_bang]

No I empathise with you and I too do not see what could be wrong. But I know I have had issues in the past and usually just start with the basics and plug directly into laptop and use the supplied capture software and take some darks which then if they are not as expected it makes it obvious if some issue with the camera but if normal then gives me some confidence and carry on trying to take bias and flats which can all be done during daylight so not taking up a good nights imaging.

I have to admit i am no expert by any means so just trying to suggest what I would do not necessarily what needs doing. 

Again I have no idea of this but could condensation inside the camera cause this ???

Steve