One of my Canon EOS1100Ds is off for Modification (Cut IR Removal) and I've been reading up about how to do Custom White Balance on it when it is back.
Everything I've read says to take the CWB image "under a clear noon sky". Where I am in the West of Ireland "clear noon sky's" are a bit like hens teeth. Particularly in October. Even less common than the "moonless clear night sky".
So I'm wondering if setting up the pic with the 18% grey card under a daylight lamp would be effective. Anyone with any experience of this?
Thanks
David
Lots of ways to do things.
Getting channels balanced is not just WB, but applying distortion of tint properly.
Note to have any colors you need to expose your AP images well, clipped stars have no color info, they are max values in all three channels.....
Easy to consider if you've got a well exposed Sun-class star in your image, just WB/tint off that,
or use things like Pixinsight scripts that solve and take star specific spectral tables and objectively balance/tint one's data so it is consistent with reality......
If you've done terrestrial photography you know that conditions will affect the daylight balance and tint....
A daylight lamp meant to mimic the noon Sun spectral and a gray card will do....
Keep in mind the whole point of calibration.
If one takes a still of a gray card under noonday Sun,
and a still of the same gray card under overcast conditions,
one can easily determine the WB/tint offset......
The whole point of using a known source like a graycard is to eliminate the variable of lighting that changes things,
thus knowing a neutral gray will have neutral values with even lighting is probably easiestkey.
You can easily use the color picker in PS to test this out. If you balanced to the neutral gray, the neutral gray will have the same RGB values across....
However,
color is more complex and the CWB is just a simple trade-off v. a willy-nilly no-care attitude.....