Arca Swiss B and I'm not sure what's going wrong

[fump]

I recently picked up my first LF camera, the aforementioned Arca B, and a couple lenses: a Fujinon S 150/5.6 and a Fujinon S 250/6.7. I've been working in 35mm and MF for about 18 years now. This is my first experience, outside of pinholes, with sheet film.

Now that you have some background the problem: every frame I've shot with the back both vertical and horizontal has, at the darkslide removal end of the frame, a strip of drastically underexposed film. The image continues, it's just about 3 stops less exposed than the film right next to it. On some sheets there's an overexposed strip at the other end. I can't find any correlation between movements (doesn't matter if everything is carefully zeroed or if I went nuts with movements), lens (it happens with all of them), film holder (it's on every sheet I expose), or anything else.

I've looked fairly carefully through the front standard without a lensboard on and a developed sheet of film and I can't see any reason why this would happen. I've looked at the ground glass pretty carefully with a loupe and a pretty tight hood and that hasn't shed any light on the situation either.

I'm using a graflok 9x12 back with 4x5 holders and sheet, but it doesn't appear to infringe upon the film and that would yield an unexposed strip, not under, right?

I attached the worst example of this I have. There are minimal movements, just a bit of tilt on the rear standard to correct for the downward angle on the tripod. You can ignore the thumbprint and horrible light leak at the bottom, I rotated the back and didn't get it quite seated for this photo. Of course, I didn't notice until I was 50 miles away because it was miserably cold, wet, windy and I was rushing.

Any ideas of what to look at or why this is happening?

[agregov]

Could be possible your film holder isn't properly seated in the back standard.

[fump]

Do you mean the back in the standard, or the film holder in the back? The film holders fit snugly in the back, I've checked from both sides. It's possible the back doesn't fit in the rear standard properly, but it looks right from both sides and I don't see how it could fit differently. I'll take it apart later and take a good look at it.

[Jeff Keller]

Bellows sagging down?

jeff

[Doremus Scudder]

Remove your camera back and see if the bellows or something else is the culprit, i.e., blocking the light path somehow. Since there is a partial image there, whatever is blocking the light path is only blocking part of it. And, since the line is fairly sharp, I'd suspect that whatever it is is rather close to the film.

You are removing the darkslide all the way before you expose, aren't you?

Good luck,

Doremus