Mysterious light leak: need help diagnosing

[felipemorgan]

My Gaoersi 6x12 has a strange, somewhat consistent light leak. When looking at developed film that has been exposed in this camera, the light leak tends to appear in the lower right of the image area (if you position the film so that the image appears right side up, unreversed). The attached sketch shows the position of the light leak, and the attached picture shows three consecutive frames suffering this malady.

The strange part of this light leak is that is not in the same place each time, relative to the film aperture. It's position varies a bit between frames. I suspect this means that the leaked light is reaching the film to the side of the image area that's currently in the film aperture, then when the film is wound on to the next frame the light leak has already exposed part of the image area even before the exposure is actually made.

There's no obvious cause for the leak, and I've added some light blocking foam to the U channel in the camera back to attempt to eliminate the light leak. The foam has not helped.

Any ideas on what's causing this and how to fix it?

 

[DarkroomExperimente]

have you tried running film through the camera without taking any shots?

 

[Arvee]

I have found mysterious light leaks by setting up a small MagLite in a dark room and taken the back off and aimed the camera at the light source and moved my eye all around looking for off-axis flare. It worked for me. Sometimes, when not the obvious foam problems, it has been a shiny spot in the blackened interior.

Good luck,

Fred

 

[felipemorgan]

have you tried running film through the camera without taking any shots?

I haven't tried that yet, but will add it to the list of things to try. Thanks for the idea!

--Philip.

 

[felipemorgan]

I have found mysterious light leaks by setting up a small MagLite in a dark room and taken the back off and aimed the camera at the light source and moved my eye all around looking for off-axis flare. It worked for me. Sometimes, when not the obvious foam problems, it has been a shiny spot in the blackened interior.

Good luck,

Fred

Thanks for the idea Fred. I'll give that a try!

--Philip.

 

[Greg_E]

I would pull the lens off and use a flashlight around the back of the camera to see if I could see anything. Make sure the room is completely dark, and that you don't look at the flashlight. You need your eyes to be adjusted to the dark or you might miss the leak.

 

[felipemorgan]

Solved!

I would pull the lens off and use a flashlight around the back of the camera to see if I could see anything. Make sure the room is completely dark, and that you don't look at the flashlight. You need your eyes to be adjusted to the dark or you might miss the leak.

Thanks to all who responded. Your responses helped me think through what was happening, and I discovered that the light leak was caused by a screw hole (not filled by a screw) from the lens cavity to the film spool cavity. It's fixed now, and if you want more details, you can read about it here: http://www.philipmorgan.net/?p=52

 

[IOS]

Good fix, JBWeld is great, i once fix a transmission leak in my van with it.



Jim