Vignetting in a negative (i.e. extreme light fall off in the corners) seemingly can be caused by a variety of things - insufficient coverage of the lens for the movements used, the edges of a lens shade protruding into the negative area, or a filter on the lens. With 4x5, I never had a serious problem with vignetting b ecause I use modern lenses with tons of coverage. However, I recently started us ing an 8x10 camera and some lenses, with more limited coverage than I'm used to. The problem of vignetting is driving me crazy. I'd guess that I get some degree of vignetting in the corners of about a third of all the negatives (about 100) I've made so far. I discovered (too late) that I can't use a polarizing filter a nd step up ring at all with one of my lenses - even when stopped down to F 64 an d the bellows extended well beyond infinity, I stil get vignetting with this len s and filter. Since I contact print 8x10, any significant vignetting in the corn ers means that the negative is a complete waste (occasionally the problem can be cured by burning in the corners but usually not).
My question is: how do others deal with vignetting problems caused by either ins ufficient coverage or use of a filter (I don't use a lens shade)? I've read as m uch as I have been able to find about the problem and it seems to be dismissed b y authors saying things like "look through the corners of the ground glass - if you see anything protruding in the lens aperture, you're going to have a problem " or other things like that. The implication is that it's very easy, just kind o f glance through the ground glass and any vigneting will be very obvious.
My problem is that the corners of my ground glass are cut out and I have difficu lty seeing anything when looking through them. In particular, it's hard to see t he relatively subtle difference between the corners of the image on the ground g lass and the rest of the image. The method that has come closest to working for me has been to remove the ground glass frame from the camera back and look at th e aperture through the bellows, with my head placed at each corner of the back. Sometimes I can see that I'm going to get vignetting, but the problem is that I don't know exactly where to put my eyes when looking at each corner. It seems th at if you get your eyes at a sufficiently extreme angle to the corners of the ba ck, it always looks like there will be a vignetting problem even when there real ly isn't one. However, if you get your eyes too close to the center of the back then everything always looks fine.
Also, you need to know what you're looking for and most authors never deal with that subject. Stroebel's book has some pictures of what a vignetted aperture wil l look like (kind of like a lemon shape) so that's been the best thing I've foun d but vignetting caused by different things can apparently can cause the apertur e to look different (i.e. the vignetting caused by a lens shade doesn't necessar ily look like the vignetting caused by insufficient coverage).
Anyhow, I hope all of this is comprehensible. It's obvious that I could use some help here. Any suggestions?