Why does my Canon rangefinder show a vertical dark band at 1/125s?
Asked 3/24/2021
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On my Canon IV S2, I’m getting a straight vertical shadow along the right side of the image, about half an inch wide on a 6x4 print. It seems to happen at 1/125 second, but not at slower or faster shutter speeds. I tested multiple rolls and settings. Flash photos look normal. Could this be caused by the shutter curtains, and why would it only appear at that one speed?
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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I had a very similar thing happen 20ish years ago on my old Pentax K1000, the tensioning mechanism on the curtains was damaged and the rear curtain was traveling faster than the front curtain. Not an issue at slow speeds where the front curtain could fully open before the rear curtain started to close, but at high speeds the rear curtain would "catch up" with the front curtain before the front curtain had fully opened.
My situation was that over 1/250 the curtain would catch up about 55% across the length of the frame.
Sadly, I didn't know this and got back from a month-long overseas trip with about 1/3 of my images missing the right half.
Obviously not quite the same thing, but there are a few other mechanical issues that could cause similar situations with out of sync curtains. For example, the curtain "catching" at that speed due to the position of the internals and getting jogged into its final position by the rear curtain closing against it.
Originally by user68136. Source · Licensed CC BY-SA 4.0
user68136
5y ago
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Generated from our catalog & community — verify before relying on it.
Yes — this points to a focal-plane shutter curtain timing problem. A dark vertical band on one side of the frame usually means the rear curtain is catching up to the front curtain too soon, so part of the film is getting less exposure.
That matches the community experience: at slower speeds, the first curtain can fully open before the second starts closing, so the frame exposes normally. At higher speeds, the curtains form a moving slit, and if curtain travel or tension is off, one curtain can overlap the other unevenly and create a band on one side.
If it shows mainly at 1/125s, that likely reflects a mechanical timing issue that becomes noticeable at that specific setting rather than every speed.
Because flash exposures are fine, that suggests the issue is with curtain travel/tension during non-flash shutter operation, not the film or processing.
Most likely cause: shutter curtain synchronization/tension needs service (CLA/repair).
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