Used the Flat comensation multipier , very nice!

[Craig Richardson]

really improved my image, by visually adjust the "flat multiplier" to a few individual frame then use that for that entire session/directory.

I posted details about CAlight in this images details I've been working on over the last few half decent nights

https://www.cloudynights.com/gallery/image/248933-crescent-nebula-ngc6888-7-7-25-through-7-25-25-7h24m-508frms-calib-auto06-sirilr2-dnz2v5-and150strch-gimpmergednz3/

Thank

Craig

[wols...@gmail.com]

Craig,

I glad to hear that the FLAT compensation in CaLIGHTs solved a problem for you. CaLIGHTs uses your masterFLAT and (masterDARKFLAT or masterBIAS) to establish a 100% flatfield compensation. Clicking on the 100.0 multiplier value causes a calibrated image of your highlighted image in the LIGHTs list. There is a FLAT Comp Multiplier slider that can be adjusted from 0%=No FLAT compensation used all the way up to 200%=Double the FLAT compensation. I have had to use this a couple of times with success.

Using a value more or less than 100% implies that either your FLATs and/or your DARKFLATs or BIAS frames are not ideal. My observation is that some people take FLATs that are very dim...less than 20% brightness. The dimmer your FLAT frames the more noisy and problematic FLAT compensation becomes. The important detail that led to my current practise is that your FLATs do not need to be at the same ISO or exposure as your LIGHT frames. I use an LED light table and take my FLATs while the sky is still darkening. I also use the minimum possible ISO/GAIN for my camera and set the exposure so that I get pixel ADU values that are close to 75% of fullscale. With the LeNhance narrowband filter and my 80mm Refractor, II use the maximum brightness on the LED light table and exposure of roughly 1.5 seconds. This gives me pixel values peaking out at 76% of maximum. My QHY294C camera is very linear, as are most of the modern CMOS camera so 76% is OK. SharpCap's sensor analysis says my camera has a linearity > 95%.

Using 76% ADU at the lowest GAIN for the QHY294C represents a huge number of collected photons and the more photons collected results in higher SNR in my FLATs. All this means is that with 10 or 15 FLATs I can achieve a very high quality masterFLAT with extremely low noise. If you want to read more about my LIGHT table solution use this link.

https://astrohobby.ca/2022/01/21/my-light-table-solution/

Peter

[wols...@gmail.com]

Craig,

I couldn't find anything in Google groups that would allow me to edit a post...frustrating. Ironically I was able to correct the spelling in the title of this post. Not a great solution but it's something. Be sure to correct your spelling in the title when you post next on this topic. Anyone following this topic will see the correction.

Rotating a master is an interesting thought. This would only apply to FLATs to attempt to correct for a unexpected camera rotation. I have never attempting this because FLATs are fussy w.r.t. vignetting and dust motes. I have always taken FLATs every time I use my system. Some background info about CaLIGHTs masterFLAT...actually all CaLIGHTs master files. All the CaLIGHTs masters are RAW(not debayered) 32b floating point fits files. If you change the file type from MSTR to FITS you can use any program that supports FITS to view them. The real issue is finding a program that will rotate a fits file and not attempt to debayer the data. RIght now I don't want to add this to CaLIGHTs. I might create a separate app for this but it wouldn't happen until the winter.

I have never considered calibrating multiple directories of LIGHT frames at one go. I am in the process of modifying the Sky Glow Comp feature so that you can specify the html calibration file from a directory where you have already calibrated the LIGHT frames. This would allow you to use the Sky Glow Comp setpoint values from one evening's imaging to compensate for changes in sky background brightness on another night. Obviously the selected filter would need to be the same. This "might" make it easier to stack multiple nights of images of the same DSO because the sky background brightness would all be the same. I know that DSS does have something similar but it also applies a data normalization which tends to bloat stars. You can read more about this issue via this link. It's the ground work I did that eventually became CaLIGHTs Sky Glow Comp.  https://astrohobby.ca/wp-content/uploads/2021/01/Deep-Sky-Stacker-Background-Calibration.pdf

I don't know when I would be releasing this update...most likely in the winter. I do most of my development work in the winter.

Peter