Flat Frame Problem in PixInsight?

Reggie Jones

Hi Adam; have a problem I've not encountered before and I'm not sure if it is with PixInsight or with my image capture software.  I took flat frames as usual after getting M51 data using Sequence Generator Pro (SGP) image capture software and the QHY 268C camera (OSC - 16 Bit) with a UVIR filter.  This camera has been tricky to get flats with; unless I've set the ADU to just below 12,000 ADU, I'll get a completely overexposed (white) flat image with no detail as you would expect.  In this case, the flats are just 1.16 sec of exposure which is much shorter than what I'm used to.

I've attached one of the flats (1st file attached) and it looks reasonable.  However, when I loaded the flats into PixInsight, they are completely dark (2nd file attached).  I went ahead and processed my images using WBPP and I got the result which is the 3rd file attached; its as if the flats didn't exist (3rd file attached).

I've spent time experimenting by taking flats with this setup using multiple ADU settings (4,000 ADU to 40,000 ADU) and even over-exposed, they still come out very dark in PixInsight.

Have you seen a problem like this?  Any thoughts or ideas?  I'm guessing my next move is to create a synthetic flat but I'd like to try to find out what may have happened here.

Thanks; Reggie

BlockHead

Hi Reggie,

What you are describing is a situation where the sensor (or data) is not actually 16-bits...yet you are telling me it is! So I do not know an easy answer based on your description of the issue.

-the Blockhead

Reggie Jones

I was afraid you were going to confirm that - this camera is specified as native 16 bit A/D but it hasn't really performed that way at least when taking flat calibration frames.  Have to do more research on this problem with others who use this camera.

Thanks for the info.

Reggie

Roger Smith

Reggie,
High camera gain setting reduces full well depth. Bit depth (ADU) is tested at minimum gain.
Roger