Finding Light Leak Source: Help Please

[G Benaim]

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

[Ralph Barker]

To check for or find the leak, try taking the lens board off, and then use a small intense light, like a MagLite to shine around the back at different angles while you look inside the bellows. The banding effect sounds like light is passing through a series of grooves, or reflecting off a grooved surface. If you can scan one of the negs, it would be helpful. One of the other Gowland users may have better ideas as to specifics, though.

[G Benaim]

Ralph,

I tried that, and there was no light at all coming through.

[Eric Biggerstaff]

GB,

A flash light might not be strong enough. I use a 25 watt appliance bulb at the end of an extension cord with a socket. This is all available for under $10 from a local home store. This is a very bright light that you can feed down the front of the camera, make sure the bellows if fully extended and of course the room is dark. I had similiar bands and it actually turned out to be the bellows.

I used the flashlight method once and thought it would be OK, but I was still seeing light leaks. When I switched to the 25 watt bulb, I found many leaks in my bellows I did not know were there. Also, with a more powerful light set up ANY light leaks from the camera will likely show up.

You might try this and see if you can find any leaks. Also, if you think it is coming from the back, take the camera into bright daylight and make a test exposure in your normal method. After that, take another with your darkcloth draped over the back and bellows, then process the film ( you can just use some dektol in a try for a few minutes if you have a darkroom, won't take long). If one has bands and the other doesn't then it might help pin point the problem. Many people get in the habit of always draping the darkcloth over the camera back to eliminate the potential for light leaks.

Hope this helps and best of luck.

[G Benaim]

Hi Eric,

I tried the lightbulb and no leaks. I'll try the other method tomorrow. I took a look at your site, and was curious whether you found much of a difference between the 150 and 210 lenses. I'm debating whether to get a 210 or go straight to 300, as I have a 90 and a 150 right now.

[Eric Biggerstaff]

I would go 300mm (even though I probably use the 210mm 75% of the time these days). The 300mm will give you a real nice 3 lens set up and then you can fill in the gaps if you want later. Not knowing what you like to photograph it is hard to say but if it is stuff similar to what I enjoy then I think you would find that set up a good one.

Good luck with the light leak issue, those things can drive you nuts!!!

[bobjames]

What types of bands are you getting? Dark or light?
Do they extend past the image area to the edges of the film?
What method of development are you using? How do you agitate?

[G Benaim]

Hi Bob,

They're dark bands, always on the upper long side, regardless of orientation, which makes me suspect the spring back. I dev in a patterson tank, rolled up negs. I took a shot w eerything under the darkcloth and still got them.

[Ralph Barker]

The forensic evidence is starting to accumulate. (Insert dramatic music and Marg Helgenberger here. ;) )

Questions: at what point did you cover the back of the camera with the dark cloth (before or after pulling the dark slide?), and where do the dark bands start? (at the edge of the film, or at the edge of the image area?)

[G Benaim]

The bads start at the ckear edge of the film, always on the same side of the sheet. If it's horizontal, it appears on the top, if vertical, on the left, but always on the same long side. I covered the whole thing before removing dark slide.

[Ralph Barker]

It seems to me that if the fog bands start at the edge of the film, the film is being fogged either prior to loading, or from defective holders (i.e. the center seam has come partially unglued or delaminated, leaking light around the edge of the septum. If the dark cloth covered the whole back before removing the dark slide, there should be no fogging resulting from a loose spring back. Absent the dark cloth, any fogging should be starting at the edge of the exposed image area, not at the very edge of the film, which would be covered by the guide rails inside the holder.

Again, a scan of the full negative or of a contact print would be helpful.