I have a 5d mark iv which was purchased in 2018. I have never had the need to use use super slow shutter speeds until now. I’ve been shooting 1/8 and under. I’ve noticed this black swooping line appears in the bottom right/middle. It doesn’t stay in same spot. I’ve never had this problem when shooting faster shutter speeds from 1/60 and up. I first noticed it when using the sigma 14-24 lens and it also appears when using the sigma 50mm. I cleaned the camera which didn’t make a difference. Any help would be appreciated!
What do you mean by cleaning the camera. Was the image sensor cleaned. That looks like it may be hair on the image sensor. Since you mentioned that it happened with 2 different lenses. Its unlikely the lens itself is the problem. Canon's lens correction DOES NOT WORK with 3rd Party lenses. The manual states that it should be turned off when using 3rd Party lenses.
It could also be a hair on the mirror that swings up when cleaning the sensor. It really looks like an eyelash.
EDIT: hair on the mirror won't show up in actual pic.
It does but dust or hair doesn't move around on the image sensor though. It usually stays in one place on the image sensor. Live View can easily prove that theory too.
I suspect that it could the early warning sign of a failing shutter, especially if it happens with all lenses regardless of brand.
I agree. The 2nd or rear curtain is likely on its way out. "I’ve been shooting 1/8 and under." "I’ve never had this problem when shooting faster shutter speeds from 1/60 and up." So this makes more sense now after reviewing the image. Then from what the OP said in the opening post.
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If something was there it would be visible at ALL shutter speeds then. With the OP using 1/60th sec or slower the 2nd curtain is also being used. Also if something was on the mirror than you'd likely see it in the viewfinder too. Since it bounces light up to the viewfinder.
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