What causes sprocket-hole shadows on a single 35mm negative frame?
Asked 6/12/2021
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I shot a roll of Ilford HP5 Plus 400 in a Canon AE-1 Program, rated at 800, then developed it in Ilfosol 3 and scanned it on an Epson V370. One frame shows dark smudge-like shadows that line up with the film perforations, while the rest of the roll looks normal or much less affected. The pattern is also visible on the negative. What is this effect, and how can I prevent it in future rolls?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
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It's called "light piping" and it is due to some minor/cumulative light leak/exposure. Films with a polyester base are more prone to it, as is B&W positive film.
The only thing you can do to minimize the potential of occurrence is to store the film with as little exposure to light as possible (before loading and after exposure).
https://filmphotographyproject.com/content/howto/2019/05/light-piping-prevent/
Originally by user70370. Source · Licensed CC BY-SA 4.0
user70370
5y ago
0
Generated from our catalog & community — verify before relying on it.
The two most likely causes are:
-
Light piping: light travels along the film base from the leader or roll end and shows up near the sprocket holes. This can affect only part of a roll, especially if the film was exposed to light during loading/unloading or storage.
-
Agitation/processing marks: on thinner or underexposed frames, developer can flow more strongly around the sprocket holes, causing density changes that mirror the perforations.
Because it appears strongly on just one thin frame, processing agitation is a plausible cause, but light piping is also a known source of this exact perforation-related pattern.
To reduce the risk:
- load and unload film in subdued light
- keep exposed and unexposed film out of bright light
- process with consistent, gentle agitation rather than overly vigorous agitation
- inspect the rest of the roll; if weaker marks appear on other frames near sprocket holes, that supports a processing cause
So: it’s most likely a perforation-related artifact from either light piping or uneven development around the sprocket holes.
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