Issue capturing flat frames with DSLR.

[mmarsie]

This is the first time I've ever encountered this issue when capturing flat frames.  I am using a Canon 1200d at Iso 400 with a Rokinon 85mm f1.4 at f2.  I was taking my test flats and took an exposure at every stop from 1 second all the way to 1/10th of a second and loaded them into PI to check the image statistics. The median and Maximum value for every single exposure were both exactly the same at 3825.  I'm loading the raw files into PI as monochrome images with the PURE RAW settings enabled in the format explorer.  Can anyone give me any advice on what is going on?  I'm totally dumbfounded.

[vicent_peris]

All yours flats are saturated. Your 12-bit camera saturates at 3825 ADU. Shoot shorter exposures.

V.

[mmarsie]

Thanks so much man, I really appreciate the help

[mmarsie]

All yours flats are saturated. Your 12-bit camera saturated at 3825 ADU. Shoot shorter exposures.

V.

Should i shoot for 50 percent of 4095 for and ideally exposed flat or just any exposure that the median is roughly 50% of the maximum value?

[vicent_peris]

If your camera saturates at 3825 ADU, you should find the exposure that gives around 1900 ADU. Please take into account that usually the shutters in DSLR cameras are not the best in precision. I think it strongly depends on your camera, but I have had problems with flats shot at a high shutter speed because the exposure lacks uniformity along the sensor.