Help diagnosing and Fixing Light Leak

[gbenaim]

Hi all,

I'm getting diagonal parallel bands at the negs edge, not sharp but definitely bands. By elimination, I'm pretty sure it's happening because of the fit of the holders on the back. I've gotten similar leaks, in different holders, in different places along the edge. I've gotten them in wood as well as plastic, new and old. I also dev'd a sheet to check that the film wasn't pre-fogged, and it came out clear. I checked the bellows twice, and no pinholes.
So, two questions: how do I check, and how do I fix? I thought of trying to block out light from the back, not expose the sheet but open the dark slide. I'm also not sure what to do when I confirm that the problem is the back fit. This is a Gowland pocket view w a spring back, and I've gotten leaks in both the horizontal and vertical positions of the back. It may just be my technique, as these are the first few shots I've taken in LF. How do you know when the holder is seated properly? Any and all help is appreciated.

GB

 

[Donald Miller]

If I were you, I would take the camera into a darkened room...remove the lens board and insert a light into the opening and insert a holder into the back...see if there is light coming around the holder at any point. Then remove the holder dark slide and see if you have light coming past the light trap.

 

[gbenaim]

I just tried that Donald, and no light comes through.

 

[James Glaze]

GB: I have been using a 4x5 for a number of years and never had a problem like you describe until the last outing. I observed the same parallel light patterns on one of my older wooden carriers. I will try the light leak test suggested by Donald. However please post if you can figure out the cause. I would not like to think I must chuck my aged but previously reliable old wooden holders yet. I am hoping it is just a screw-up in getting the holder seated

 

[Campbell]

I've never met Peter Gowland but I've read about him. He's supposed to be a very nice guy and anxious to help when anyone has a problem with one of his cameras. Since you think you know that the problem is with the camera back I'd suggest that you call him and see if he has any suggestions.

Is there by any chance something protruding from the top or sides of the camera that might be causing the back to stay ever so slightly open? I attached a bubble level on top of a Tachihara and got it just a fraction of an inch too far towards the back, which caused it to hold the back open just enough to let light in when the back was supposedly closed.

It's hard to explain how to tell if a holder is properly seated. You pretty much just "slam" it in until it goes as far as it will go. You might look at the location of the base of the holder when it's in the camera just to see if everything seems to be lined up and that there are no obvious gaps anywhere.