Mystery of subs being darker than bias

[Gastraea (John)]

Hi All
I'm still in the process of investigating this mystery but I thought I would see if anyone had any clues.

I've recently discovered that my bias and dark frames have pixel values that are greater than the values in my 300s subs.

I'm not sure how this is possible. I have looked at the "settings" text file that accompanies the .fits file and found the settings to be the same in both. The bias frames were taken on a different computer so this may be it? Who knows.

Anyway I have checked the subs are in fact 16bit (some values are 64k) and some of the lowest values are around 64 or 80 but the bias frames and darks are all around 500 ish. Not sure what the hell is going on.

I have multiple nights shooting sub in both png and fits and all of the subs have values lower than the bias frames. Driver issue???

OSC is ASI2600 and capture is sharpcap pro


There is something about Display Black Point etc shown below I'm not sure what this even is.

in subs
Display Black Point=0
Display MidTone Point=0.001
Display White Point=0.01171875

in bias
Display Black Point=0.005859375
Display MidTone Point=0.006859375
Display White Point=0.506859375

[Gastraea (John)]

I've been able to replicate the issue.
I have been capturing subs with an intel nuc and for some reason with sharpcap in this thing it gives strange values.
Not sure I can make sense out of this at the moment.
ASI studio seems to capture bias frames with values around the 500 ish mark but sharpcap seems to get subs with values of 0 and 16, too weird!!

Not sure I want to spring for an upgrade to the nuc.

Still under investigation.

[Gastraea (John)]

Strange beyond belief. The ASCOM driver is the same, on the nuc I get values more like 16 but on my laptop I get values like 500. Yet ASIstudio on the nuc gives values like 500 too.

I think this is somehow sharpcap related. I might look to wipe the nuc and start again. This is too weird.

[The_bluester (Paul)]

Is there an editable "Offset" figure in Sharpcap? I would imaging ASI studio would default to ZWO's normal offset of 50, which will change your values compared to an offset of 0.

[Gastraea (John)]

Originally Posted by The_bluester

Is there an editable "Offset" figure in Sharpcap? I would imaging ASI studio would default to ZWO's normal offset of 50, which will change your values compared to an offset of 0.

I went looking for such a setting but to no avail. I'm just reformatting the nuc at the moment and will do a fresh install of everything. Hopefully this resolves the issue.

[Gastraea (John)]

Well I reinstalled everything and it DID fix the issue.
So who know what that was all about.