the double shutter speed rule ruins your video

Started 6 months ago | Discussions thread
Sean Nelson
Sean Nelson Forum Pro • Posts: 15,158
Re: the double shutter speed rule ruins your video

Svetlov Misha wrote:

Sean Nelson wrote:

Svetlov Misha wrote:

CanonUserG40 wrote:

Why are you still refusing to accept that CMOS sensors output line by line? The process of digital image capture has been explained to you ad nauseum but you still seem to think you know better with your crackpot "experiment"..

i see what i see: i push flash button with ultra short impulse and i see the frame totally illuminated. those impulse duration 1/10000 is much shorter sensor readout but still - all the lines illuminated, not the half, not the quater, but every single of 1080 lines recorded.. so, what about lines? why?

You are confusing the readout with the exposure. When the flash fires, it dumps photons onto the entire sensor all at once, storing charges in all of the photosites. But it takes time after that for the camera to read out the charge values.

If you're using a high shutter speed, then some of the rows are going to be cleared after the flash fires and when those rows are read out then you won't see the flash in them. But if you're using a slow enough shutter speed then the charges may be held long enough that they can all be read out after the flash has fired. It depends on the timing between exactly when the flash fires and where the camera happens to be at clearing out some sensor rows while reading other ones.

so, getting all the frame long exposured is better than half of the frame only?
the equal shutter is better than double?

It depends what you're trying to do. The so-called "180 degree shutter rule" is a compromise: it allows motion to blur enough to help mask the staccato effect of low frame rates but not so much as to smear everything into mush. If you're shooting relatively static scenes then you might use a much higher shutter speed so that you can open the aperture up to reduce depth of field, and if you're shooting in very dim like you might use the longest possible exposure so as to minimize noise. Those are two examples plucked from a universe of choices.

Everyone is free to choose whatever shutter speed they feel best gives them what they're looking for. Choice of shutter speed is just one small part of the creative process.  Telling people they must never follow the 180 degree shutter rule is just as bad as telling them they must always follow it.

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