SharpCap Forums

Version: 4.0.9224
Camera: PlayerOne Saturn 533MC

This camera is supposed to have no amp glow. So no need to take darks. Because of this, I figured I could use "Hot Pixel Removal Only" for "Subtract Dark" and my flat. But when I do this I will see a slight reverse vignetting. Here is an image with exaggerated stretch to show it.
If instead I create a dark and apply it, I get this. Again exaggerated stretch.
You can download the fits, flat and dark files from here: https://1drv.ms/u/s!AmzOfpCoABCRgdZdVE_ ... w?e=V8meHN

Thanks,
Cey42

Hi,

darks are really necessary for using flat frames, since you need to remove the background offset level from both the image data and the flat frame data before applying the correction. Failure to subtract the offset from the light frame leads to over correction as is seen in your sample.

SharpCap will do its best to fudge this requirement for you providing you capture your flat with the bias or dark flat option enabled. In those cases SharpCap will put a percentage value at the end of the flat file name - that is the brightness level of the background offset. If you use a flat with that info in the filename with no dark, SharpCap will apply a constant offset based on that value. I can see that your flat frame doesn't have that info in the filename, so either you created the flat in some other way, or did not use bias/dark flat, or perhaps renamed the file?

cheers,

Robin

Thanks for the info. I did not create the flat with a bias or dark. I will do so next time.

Cey

Creating a flat with bias solved the issue.

Thanks,
Cey