# Shutter slower than video FPS

I'm trying to shoot low light video on my RX100 m3 and I want to make the best of it. So it would make sense that the ideal setting (in many cases) would be to open the shutter for as long as it can be open for that frame. So if recording at 25 FPS video, then you would have the shutter open 1/25 seconds. That way you get max light in.

However I notice my camera doesn't mind having the shutter way slower than that number, I guess that means that it actually spills same information onto several frames?

If I set it to 1/25 does that mean absolute maximum. OR does the camera perhaps need a few milliseconds between each frame and therefor 1/25 for 25 fps video is too slow?

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"If I set it to 1/25 (shutter speed) does that mean absolute maximum (or lowest setting)?" Yes, if it was a non-digital video camera. This rule applied to the old non-digital (film) video cameras where you cannot set shutter speed lower than the frame rate.

Meaning that one celluloid was exposed for the full 1/25th of a second. Assuming 25fps.

For digital video cameras each frame can be blended with the other. This technique allows you to film in low light situations at the expense of motion blur. It can be used to create what some called a dream like sequence.

You should just view this as another creative control that you have to managing low light situations or adding motion blur to your videos.

See example below:

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Any ideas on the second part of their question about determining at what point this starts happening? It seems like one of the main parts of the question was trying to determine what the slowest they could go without overlap is. – AJ Henderson Jul 18 '14 at 13:49
@AJHenderson That second part, I would assume no, it does not need to a few milliseconds between each image. But then I remembered the rolling shutter effect. Each image is never recorded instantaneously like a CCD sensor (Most video cameras are now CMOS sensors). So there is a few milliseconds taken for that as it scans from top to bottom, and I noticed the effect is more evident for full frame sensors as opposed to the smaller sensor sized cameras. I don't know enough to answer that with any conviction. Need to read up on some technical specs to find out. – eLouai Jul 19 '14 at 4:33
Fair enough. I wasn't sure either. I know that the light Wells need to be emptied and this takes time but I'm not sure how long. – AJ Henderson Jul 19 '14 at 12:09

I don't know this model, but in general video cameras don't use a physical shutter, but an electronic one. The aperture is always open and 'shuttering' means limiting the exposure time through blanking. So a setting less that the frame rate is effectively 'off'.

As for 'spilling the same info onto several frames', that's only true if there's no motion in the shot. If there is, adjacent frames capture different images -- different moments in time. What shuttering can do is limit the blur caused when there's motion during an exposure. It effectively freezes the action.

In any case, assuming they're synchronized, lowering the shutter speed matters only until you reach the frame rate. After that it should have no effect.

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