Another question re the elusive FLAT and Bias Frames

[batema (Mark)]

Hi,

I am using a QHY-9 mono camera and last night shot M83 making sure everything is ready for astrofest next weekend. I shot my RGB at 2x2 bining so when it came to using Al's Virtual lightbox on my laptop I took my flats for RGB at 2x2 bining. Is this correct and I took flats for all my colours at this setting so the histogram was about 1/3 from left.

I also took Bias darks at 1x1 binibg for my Lum and 2x2 for my colours but set the time for one second as I thought I has read somewhere that if you set the shutter speed for 1/1000 sec the camera can not handle it. Any way when I processed I had a horrible gradient through my image that disappeared when I only stacked LRGB and the corresponding darks without flats or bias frames.

Thanks

Mark

[marki]

Hi Mark

Yes you have to shoot your flats and darks at 2 x 2 bin if that is what your lights are. I find the best results are between 20 -23K ADU for flats on this camera when the offset and gain settings are correct. That said I have had a stack of problems producing decent flats in 2 x 2 bin mode with the QHY9 using the old drivers, so much so that I dont bother using bin modes any more shooting everything in 1 x 1 bin. I have not tried to see if the new drivers have corrected this but I am sure Robin (Tandum) will have more to say about it. As for exposure times the QHY9 shutter is very slow and a 1 sec exposure will leave artifacts which cannot be removed. I try to set my illumination to get my flat exposures at about 4 sec in the 20 -23K ADU range. Hope that helps.


Mark