Here you go Andrew:
http://tech.groups.yahoo.com/group/d...message/158253
What he was referring to was nonlinear were his flats with a D800. He is saying that the RAW can shift.
I am not sure about his flat fielding techniques, they seem a little odd to me so perhaps he is right perhaps he is simply doing his flats in an odd way. Its hard to tell. So that may or may not be an issue.
Certainly the resulting image is very good. So his work around was good.
Flats was a topic I found out more about at AAIC and found a few tips on it that may help.
Firstly he recommends to rotate your instrument to get rid of gradients - I have never heard of anyone else ever doing that so he must be using a very uneven source of light for his flats. Secondly he subtracts a number for bias instead of an actual bias shot. I don't think that would be ideal either why subtract a theoretical when you can have the actual?? So, keep that in mind.
Greg.