Light Leak Theories

[Kleiny41]

Yesterday I developed 6 negatives in BTZS tubes. I used a relatively new 11x14 frame dark-bag so I had room to switch the caps.
2 of my negatives were perfect, 4 had a square-shaped over large centrally located over exposure spot covering most of the negative. The only thing that makes sense to me is I could have a major light leak in my traditional Sinar bellows. All summer I’ve used only the double bag bellows and I think I’d switched back to traditional for a bunch of these shots. I haven’t done any light leak testing but I was curious if this shape of over exposure marking had any recognizable characteristic clues recognizable by more seasoned analog photographers?

Many thanks!


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[Steven Ruttenberg]

Looks maybe like a darkslide issue or bellows interference judging by same pattern. Are you sure film was loaded in holder correctly? One thing happened to me once is I had taken the ground glass holder off camera, and wgen I put back in i put it on 180 degrees out. So film should have been inserted from keft, not fight, but I inserted from right and ended up with negatives look like these. Justva rhought. Is your back on on way you normally use and film holder inserted from proper side?

[Two23]

Agree with above. Yesterday I screwed up and didn't get the film holder pushed all the way down into the back and there might have been a small gap. It doesn't take much to create a big problem.


Kent in SD

[Kleiny41]

I just tested all my bellows with Polaroid film and it definitely isn't a bellows issue. I haven't changed my ground glass or back position but it could be my film holders were not properly seated. I also have a 90mm Fujinon that is in a Pronto shutter. Only has 1/100, 1/50, 1/25 and Bulb. I don't see the same pattern on the Polaroid shots but it definitely tends to overexpose images-timing might be off. I'm going to look at all my variables again.

[chassis]

I had a phase where I experienced light leaks from improperly seated film holders. It's not uncommon.

[Louie Powell]

I once had a problem with light leaks when using a Polaroid 405 holder. The leak produced fogging along the short edge of the sheet. It turns out that the problem was that wire handle on the darkslide was very close to the back of the camera, and when I pulled the darkslide, my fat fingers inadvertently lifted the holder away from the camera back.

The point is that the cause of light leaks can be very subtle and not at all obvious.

[Maris Rusis]

Do I see some negatives with black edges? If so this means that the film was light struck before it was loaded into the film holder or after unloading from the film holder. If the film has some rebate edges clear this means the film was light struck in the camera or the film holder is defective, cracked, bad light trap, .... ?

[Kleiny41]

I checked those negatives when I got home from work and there is some evidence of extra exposure on the edge where the notch code is. That’s the only edge with evidence of extra light.


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[Steven Ruttenberg]

Thirc negative from top has a weird squarish looking object in it. The more I look st these nakes me wonder if they weren't double exposed.

[schafphoto]

The best way I have found to check for light leaks in LF cameras is to remove the lens from a #1 or #0 lens board and stick a light socket into the hole, so it protrudes into the bellows backwards. Tape the socket in with black tape. Put a LED or CFL bulb inside the camera, put your questionable film holders in the back, turn on the bulb in your camera and turn off the room lights to complete darkness. If you have light leaking from your bellows, camera, standards, film holder or light traps, you will see it after your eyes adjust. You can rack the bellows in and out to the point where the bulb almost touches the film plane to check your holder seals with the dark slide out. Then flip the holder and try the other side. Extend the bellows all the way out and check for pinholes in the bellows corners and full attachment where the bellows meets the standards.

SOO much easier than putting a flashlight inside the camera. Don't use a tungsten bulb, it will get too hot and melt something. I like the crappy curly cue 13W CFLs (60W equivalent with the CFL crop factor).

Eliminate the camera and holders first. I do this enough that I have a plastic lamp socket with a screw in retainer and an 8' cord that I keep just for this purpose.
Good luck!
-Schaf