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I film a lot with the Canon C100, I've noticed that when a lot of flashes are going off I get a lot of image issues (which I think is due to how CMOS exposes line by line) (see picture), the effects are more pronounced in slow motion (the c100 only shoots interlaced).

I have a few questions:

whats the technical name of this 'effect'/issue

why is it more pronounced in slow motion (does interlacing effect this?)

and is there anything I can do with regards to shutter/speeds or utilizing 'clear scan' in the c100 to reduce this?

enter image description here

  • is it the horizontal lines you're talking about? That looks like the exposure changed during the scan. changing shutter speed might help. – stib Apr 8 '15 at 6:26
  • I think you're talking about the "rolling shutter" issue, where each frame isn't a snapshot of a single point in time. Rather, each line is from a different moment, or something like that. A flash going off will then lead to tearing, like you'd get in a game with vsync off. – Peter Cordes Apr 11 '15 at 13:39
  • also: They make cameras that only shoot interlaced? Yuck. I'd take lower rez progressive at double frame rate any day. (e.g. 720p60). – Peter Cordes Apr 11 '15 at 13:44
  • @PeterCordes yea the c100 mk i shoots interlaced 60/50i, everything else is progressive. its a pain in the ass, but not worth upgrading to the mk ii for. but yea rolling shutter is indeed it, I kept searching after I posted this. It seems like theres not much one can do – Alex Apr 14 '15 at 2:32
  • If you really want to shoot content with strobe/flash lighting happening, there might still be cameras made that don't use a rolling shutter. IDK, and that doesn't help fix the video already recorded. – Peter Cordes Apr 14 '15 at 2:46
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whats the technical name of this 'effect'/issue?

The horizontal lines are likely caused by an effect called Rolling Shutter

why is it more pronounced in slow motion (does interlacing effect this)? I would have expected interlacing to reduce the visibility of the effect iff it was done on a line of pixels at a time. However, if bands of pixels are read during the interlacing, that might make the effect worse. That would provide a stripe of pixels at a similar exposure level and a step change when the next stripe was read.

is there anything I can do with regards to shutter/speeds or utilizing 'clear scan' in the c100 to reduce this?

I don't believe so. It is usually related to lower light levels so anything you can do to get more light into the camera would help. You might find that reducing the exposure time (faster shutter speed) might help as it would force the camera to complete all the scan in less time.

(Seems a bit unsporting to use some of the question comments as an answer but they matched and expanded on what I knew.)

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