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Digital Slow Motion


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#1 Sol Train Saihati

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Posted 08 January 2007 - 08:24 AM

Simple question: Is it necessary to open the aperture when shooting slow motion on digital formats?
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#2 Alex Haspel

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Posted 08 January 2007 - 08:59 AM

Simple question: Is it necessary to open the aperture when shooting slow motion on digital formats?


if you shoot with a video camera that is only capable of 25fps or 50i and you add the slowmotion in post, then no.
if you shoot with a video camera capable of variable frame rates like the hvx200/varicam/etc then you have to compensate for the exposure loss one way or another. you could do this opening the iris, adding more light or using digital gain.
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#3 Troy Warr

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Posted 08 January 2007 - 09:08 AM

Simple answer is yes. The laws of physics still dictate that each time you half the exposure time of the CCD/CMOS, you have to double the light passing through the aperture. In this sense digital is no different than film.

But, in practice, I don't think it can be quite that simple. I think it also depends on how the camera generates its slow motion, which isn't always in exactly the same way as a film-based camera. The Sony HVR-V1U, for example, shoots a burst of 240 fields (not frames) per second, so I would assume (and somebody please correct me if I'm wrong here) that you wouldn't need to compensate for the reduced shutter speed by opening the aperture as much as with a film camera, on that particular camera. Ultimately, though, you're still bound to the laws of physics.
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#4 David Mullen ASC

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Posted 08 January 2007 - 12:51 PM

If you change the shutter speed or frame rate in the camera, you have to compensate for the exposure. But if you don't and create the slow-motion entirely in post, then you don't have to adjust the exposure.

However, most people converting 60i/50i footage to slow-motion in post will at least shorten the shutter speed to reduce motion blur on each field, like to something like 1/100th of a second -- in which case you would have to account for the exposure loss from shortening the shutter speed.
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