Uneven exposure problem

[derekh]

I just made my first attempt at some pinhole photographs. It was also my first attempt at hand processing 4x5 sheet film. I seem to have a problem with uneven exposures. Each image has a light band running down the length of the negative (see attached image). I don't think this is due to light falloff; if that were the case I would expect the brighter area to be circular, whereas in this case it is a linear, straight-line thing. I shot both portrait and landscape images, in both case the brightness runs down the long axis of the negative. Anyone had this problem before? I'm not sure whether it is caused by the optics, or maybe by the way I developed my negs. The negs were developed in a tray, I did 5 of them together. Although I "shuffled" the negs continuously during development, I'm thinking that maybe the negs stuck together and got more developer along the edges that at the centre.

 

[pgomena]

Derek -
If you are using a semicircular pinhole camera (round tin, oatmeal box, etc.) that curves the film, and if you are using a film that has a shiny surface (no retouching texture on the emulsion side), the film may be reflecting light onto itself. I had this happen when using color transparency film in a large can-type camera. Tri-x has a somewhat matte surface on the emulsion side that allows for mechanical retouching, and has not caused this problem for me when used in a can-camera.

Peter Gomena

 

[derekh]

I'm using a 4x5 view camera with a pinhole lens, so I don't think that could be the problem. Thanks for the suggestion.

 

[Lee L]

Is your pinhole in bare, reflective metal? If so, try "smoking" it with carbon from a candle flame or blacking it with a black permanent marking pen. Was the sun directly overhead? You may be seeing reflected light off the pinhole edges.

Lee

 

[Soeren]

I did some lithprinting a while ago (my first atempts) The first papers I ran through I agitated continiously resulting in a dark band across the image. Whether it was a standing wave or what, I don't know but cutting the agitations to a minimum solved the problem. That was in the positive process so.......
Søren

 

[Charles Webb]

Peter,
FYI Mechanical or pencil retouching is not normally done on the emulsion side due to the fact that each stroke of the pencil will be in focus when the negative is printed focusing on the grain. The retouching on the base side is slightly diffused by the base thickness of the film thus the retouching does not show as sharply or at all in the finished print.

 

[pgomena]

Good point, Charles. It's been a long time since I've retouched a negative. Yes, the "tooth" for pencil retouching is on the back side. Is dye retouching for b&W not done on the emulsion side? Hard to remember since the last time I did it was 15 years ago.

Some B&W films are very reflective/shiny on the emulsion side. Tri-X is less so than other films, which is why I've not had problems in "can" type pinhole cameras. I think Bergger 200 also has a fairly matte emulsion surface. I ran into trouble with Fujichrome Astia reflecting light onto itself in a "can" camera.

Peter Gomena