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Red lines in color negative film?

I went to a good photography school for a few years and therefore do know a bit about photography. I do have some speculations as to what might cause this like light leaks when loading the film or excessive exposure to heat or sunlight. I also noticed that the rolls without it seem to have a slight higher quality of photos. So I wondered if it maybe is caused by something in the less expesive cameras.

This is really starting to bug me not actually knowing. Also I'd like to be able to tell my customers what it is causing this rather than just continue to speculate. So if anybody knows what causes this I'd really appreciate the response. Thanks.

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October 01, 2006

Red lines on color negative film. Lines run vertical. I will assume this means the lines run with the film. Actually I need more information, thin, thick where on film? Is the line seen only in D-min area? Only in D-max area? Does the line continue through image areas? A sample would be helpful.

Look at the film by reflected light. Try and examine carefully a reflection of a ceiling light on the shinny surface of the film. Twist and turn the film as you look. Look at both the emulsion and the base side. You are looking for changes in the emulsion such as swelling or scratch. This examination is for pressure marks. Pressure exposes film and yes pressure desensitizes film (depends on where the pressure is applied. The film path in the film machine is complex and pressure/scratching is common.

Fog due to light leak is a real possibility, hard to detect. Prepare and process a roll in the dark. Most labs can’t go dark so wait till night and turn off all lights before prepping the film. Keep the lights off until complete.

Film machines usually have infrared LED’s in the film path. They shine infrared light onto the film as it enters. Infrared receptors either see this energy or the energy is interrupted by the film. The pattern of what the receptors see is interrupted by chip logic to set replenishment rate. Possible the IR sources have changed color and are exposing. Normally color negative film is insensitive to IR.

Sometimes a pressure mark will only show on exposed areas. Not enough pressure to trip the film. Add pressure to an exposed area and the combination causes hyper-sensitivity and develops up as a thin line seen only when superimposed over an image area. Pressure before processing sensitizes and a line like mark develops up. On color film has a top emulsion layer sensitive to blue light. This develops up as a yellow line however the C-41 film has an orange base (auto-mask) so yellow + orange is reddish.

Pressure from rollers while the film is in the developer desensitizes. This causes a low density line. Pressure while in the developer retards development action by restricting the flow of developer as it percolates in and out and through the various gelatin layers.

When a lab is heated in fall and winter, the humidity is generally lowered. Low humidity produces a condition whereby static electricity may be present. If the machine is poorly grounded the static charge may not bleed off. Static electricity can cause fogging but the pattern is not a perfect straight line.

My guess is pressure from a roller or squeegee.

Alan Marcus
ammarcus@earthlink.net

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October 02, 2006

Jennifer

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October 02, 2006