Very interesting thanks but also leaves me somewhat confused: You said in an earlier video that the actual mean ADU of the flats isn't important as long as it is in the linear range. But here you show that minor changes in the flats can have a big result on the final image. Is this perhaps an interaction between flats and dark flats? I have never taken dark flats which I understand to be for cooled cameras (I use a DSLR)
Great question! When imaging the flats, the ADU isn’t something to overthink, as long as you are in the linear range. As long as there are no pixels reaching the maximum value for the camera (I.E 65k ADU) and no pixels showing 0 value on the minimum end and your flats are showing dust motes along with even illumination, and 1/3 to 1/2 of the histogram you’re good to go, especially because your calibration frames for the lights and flats (darks and flat darks - or bias for DSLR) will adjust this in the calibration process (see 12:08) :) Generally, when there is a flat field correction issue, it can be traced back to an issue with the dark frames. That issue could be a few things such as light leak causing ADU to be high, camera setting such as gain, offset or even temperature could cause a discrepancy. If you’re using a cooled camera and have a dark library, using an old set of dark frames or old master dark could cause a discrepancy due to sensor degradation. Taking a look at FITSheader and analyzing the statistics of the images will tell a lot of the story of what’s going on. If I ever need to adjust anything, I will always adjust using the darks and/or dark flats and doing this will, by nature, affect the flat and light frames (I demonstrate this starting at 12:08). I find this to give the most accurate results as it is natural due to the calibration process. Every once in awhile, I may need to do some small adjustments to the flat frame to fine tune it to where I need it, but that is very rare. a DSLR, using flat darks (aka dark flats) may not be a good idea, however, using bias might be a better choice due to how the DSLR behaves.
thanks fror helping me sort out one of my issues with the flats, they were not long enough and caused the overcorrection
Awesome to hear! Did your dark frames match? If so, were you able to adjust your flat instead of retaking?
@@Hidden.Light.Photography yep everything worked
Awesome, I’m very happy to hear!
Very interesting thanks but also leaves me somewhat confused: You said in an earlier video that the actual mean ADU of the flats isn't important as long as it is in the linear range. But here you show that minor changes in the flats can have a big result on the final image. Is this perhaps an interaction between flats and dark flats? I have never taken dark flats which I understand to be for cooled cameras (I use a DSLR)
Great question! When imaging the flats, the ADU isn’t something to overthink, as long as you are in the linear range. As long as there are no pixels reaching the maximum value for the camera (I.E 65k ADU) and no pixels showing 0 value on the minimum end and your flats are showing dust motes along with even illumination, and 1/3 to 1/2 of the histogram you’re good to go, especially because your calibration frames for the lights and flats (darks and flat darks - or bias for DSLR) will adjust this in the calibration process (see 12:08) :) Generally, when there is a flat field correction issue, it can be traced back to an issue with the dark frames. That issue could be a few things such as light leak causing ADU to be high, camera setting such as gain, offset or even temperature could cause a discrepancy. If you’re using a cooled camera and have a dark library, using an old set of dark frames or old master dark could cause a discrepancy due to sensor degradation. Taking a look at FITSheader and analyzing the statistics of the images will tell a lot of the story of what’s going on. If I ever need to adjust anything, I will always adjust using the darks and/or dark flats and doing this will, by nature, affect the flat and light frames (I demonstrate this starting at 12:08). I find this to give the most accurate results as it is natural due to the calibration process. Every once in awhile, I may need to do some small adjustments to the flat frame to fine tune it to where I need it, but that is very rare. a DSLR, using flat darks (aka dark flats) may not be a good idea, however, using bias might be a better choice due to how the DSLR behaves.