Hi everyone,
I recently switched from a DSLR to a QHY163m + Baader LRGB filters. My first steps went Ok, I think - but I focused on very bright and diffuse objects (M42, Rosetta nebula).
Switching to objects with a lot of sky background, I noticed that my flats overcorrect across all the channels. I understand that this is most likely caused by underexposing them. So I am now trying to understand how to fix this (don't get a lot of clear nights in these parts, so would like to be prepared for the next one, when ever that may be).
My technique so far was to use the built-in function in APT to automatically determine the correct expose for each channel. APT suggests a target ADU of 20.000. This comes out at ~18.500 when checking in PI.
Two questions:
1) So if 20.000 is too little, is there any robust way, other than trial and error, to figure out what the correct ADU should be?
2) Using Pixelmath in PI with the expression "$T+0.2" I was able to "boost" the L flat and "rescue" my luminance image. However, a similar approach (using a range of scaling factors from 0.05 to 0.5) for the RGB channels did absolutely nothing. How can that be?
Thanks for any and all input!
Marc
Example of the L channel prior to "flat boosting": https://www.dropbox.com/s/6y1wq6gmjaen5zv/L_light_gardient_problem.jpg?dl=0
and the flat: https://www.dropbox.com/s/ok163d4813mzelg/flat-FILTER_L-BINNING_1.jpg?dl=0
I recently switched from a DSLR to a QHY163m + Baader LRGB filters. My first steps went Ok, I think - but I focused on very bright and diffuse objects (M42, Rosetta nebula).
Switching to objects with a lot of sky background, I noticed that my flats overcorrect across all the channels. I understand that this is most likely caused by underexposing them. So I am now trying to understand how to fix this (don't get a lot of clear nights in these parts, so would like to be prepared for the next one, when ever that may be).
My technique so far was to use the built-in function in APT to automatically determine the correct expose for each channel. APT suggests a target ADU of 20.000. This comes out at ~18.500 when checking in PI.
Two questions:
1) So if 20.000 is too little, is there any robust way, other than trial and error, to figure out what the correct ADU should be?
2) Using Pixelmath in PI with the expression "$T+0.2" I was able to "boost" the L flat and "rescue" my luminance image. However, a similar approach (using a range of scaling factors from 0.05 to 0.5) for the RGB channels did absolutely nothing. How can that be?
Thanks for any and all input!
Marc
Example of the L channel prior to "flat boosting": https://www.dropbox.com/s/6y1wq6gmjaen5zv/L_light_gardient_problem.jpg?dl=0
and the flat: https://www.dropbox.com/s/ok163d4813mzelg/flat-FILTER_L-BINNING_1.jpg?dl=0
