Strange less-dense portion on negatives

I've now run 2 rolls of film through my 20's vintage Kodak Folding Autographic Brownie #2, both films are Adox CHS 50. On every frame in the rolls there is a section of about 1/4 of the frame that is significantly less dense than the other 3/4 of the frame. I've ruled out manufacturing defects in the film, since it's in the same place on every frame. Holding the camera in it's normal vertical format the light section is near where the top of the frame would be in the camera. I don't think it's a developer problem either, since the problem is across the width of the frame rather than the length. Looking at the camera the only possible explanation I could think of is that the very first bellows pleat behind the lens likes to flatten out or sag slightly instead of hold its peak, but I can't see that causing the problem. I saw that the problem is that 1/4 of the frame is less dense than the rest, but it could easily be that 3/4 of the frame is extra dense!

If pictures would help I can see if I can borrow my roommate's digicam to take pics of the negatives and camera. Any ideas what could be causing this?

-I would look for a aperture blade which has come loose and has made the opening out of round or off center..
-A significant flaw or some foreign material on the inner lens (the outer lens turns).
-Perhaps a piece of material from the bellows in the image frame.

What sort of shutter does the camera have? If it's a focal-plane shutter, like in most SLRs, then it could be that the shutter needs adjustment -- if one of the curtains is moving at an irregular speed, it will result in variation of exposure in the way you describe. A similar possibility is that the shutter speed might be off for flash exposures, but that would only apply if all the affected photos are flash exposures. If so, the idea is that the shutter speed might be a bit faster than it should be, so only 3/4 of the frame is getting the flash exposure, and the remaining part of the frame is exposed only from ambient light.

Justin:

I would lay odds that your problem originates with the bellows.

Can you try a couple of test exposures - one with the bellows as is, and another with the bellows manually "pulled up" in the area you expect?

Matt

I've been letting the bellows sit folded with the peak of the trouble pleat set into the proper position, so hopefully it will hold. Unfortunately I'm out of 120 film right now but I'm hoping to talk a friend of mine in to taking down to Victoria to get some in the next few days. I wish I wouldn't have written off the bellows as the problem (if it is), might have been able to save some of my good shots!

srs5694: The shutter is a very simple Kodex leaf shutter with speeds 25, 50, B, and T! As far as flash goes, the manual for this camera suggests using Kodak Flash Sheets as a safer alternative to flash powder when indoors. This was a pretty inexpensive camera even when it was made in the mid 20's. I have to say it is pretty fun using a camera that's nearly as old as my grandparents!