ATM All Vignetting the same?

["Jim Miller" <jim@jtmiller.com>]

It's not obvious to me from anything I've studied yet what the operational
difference is between vignetting at the tube entry, secondary size loss and
vignetting at the focuser/eyepiece.  Do they all have the same qualitative
feel or are some more objectionable than the others, i.e. sharp vs. slow
falloff.

I've read both Kriege and Berry and Texereau, 2nd and found no treatment.

Also is there a good discussion somewhere (book, web) of the "75% ray".

tnx
jtm