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04-19-2013, 01:10 PM   #1
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Random Q: Frame rates for camera mode versus video

Hi all

I have a question that is bugging me and can't find anything explaining it. My basic understanding of a video camera is that it is something that takes lots of still pictures every second e.g. at least 30fps. As DSLRs can also do video, how come when you are using them as a camera they can "only" do say 6fps but in video mode can do loads more?

And how come you don't hear the shutter clacking 30 times per second when taking a video?

Just trying to figure out the difference how they work given both are essentially just taking still photos.

Sorry, I know this is a very random question...

04-19-2013, 01:20 PM   #2
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QuoteOriginally posted by thechumpen Quote
And how come you don't hear the shutter clacking 30 times per second when taking a video?
Because the electronic shutter is used in video mode.

At 6fps for stills, you're generating 6x16mp images, and all that data needs to be buffered, processed, and flushed out to the memory card.

At 30fps for video, you're recording 30x2mp images, which is actually less data, so the same processor should still be able to handle it

I know that my example may be an oversimplification, but I hope it helps you understand how things work!

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04-19-2013, 01:36 PM   #3
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Ah Ok. I thought HD video would be more MP than that. Doh! Bit obvious if you do the maths.
04-19-2013, 02:43 PM   #4
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Also each still shot is like every still shot in mechanical wizardry. I may not have the exact order right, something like:
Aperture arm goes up to close the 5 to 9 aperture blades on the lens
Mirror flips up
Shutter opens, complex in itself (front and rear curtains)
Shutter closes
Mirror returns
Aperture arm moves back.

I don't know exactly how the video mode works but the mirror is not flipping back and forth for each frame.

04-19-2013, 04:59 PM   #5
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Yes, as noted, HD video is only around 2.1 megapixels. DSLRs really are not well optimized for video. Ideally, the sensor would exactly match the output resolution, which is only found in specific video cameras, like the Canon HF G10/20/30, or the upcoming Black Magic Pocket Cinema camera.

Otherwise, the camera has to interpolate pixels, or skip lines. As a result, many DSLRs have worse resolving power than your average HD camcorder.

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