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24P + Shutter


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#1 Roberto Ditleff

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Posted 14 August 2006 - 09:13 AM

Two questions :
1 How close come the 24P on a HD camera to the blurr effect of a 24fps on a film camera ? Can anybody elaborate on this , please.
2 Since I will be using the shutter on a hd camera to obtain the 24P look, how could I simulate the look of 24fps and shutter variations like 90º, 45º that we do on a film camera.
Thank you all
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#2 John Ealer

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Posted 14 August 2006 - 09:47 AM

Two questions :
1 How close come the 24P on a HD camera to the blurr effect of a 24fps on a film camera ? Can anybody elaborate on this , please.
2 Since I will be using the shutter on a hd camera to obtain the 24P look, how could I simulate the look of 24fps and shutter variations like 90º, 45º that we do on a film camera.
Thank you all


By blur effect, I assume you are referring to motion blur?

Some basics, which I'm sure you're familiar with:

Most commonly used film cameras have a rotating mirrored shutter mechanism. Digital cameras (with the notable exception of the Arri D-20) generally use an electronic shutter. The difference is that an electronic shutter is instantaneously on or off, so that the entire target area is exposed at exactly the same moment in time...i.e. each pixel of the entire frame is exposed during exactly the same "slice" of time. A mirrored shutter, since it's rotating through the frame, actually exposes different parts of the frame during very slightly different "slices" of time...i.e. the top of the frame will see a very slightly different slice of time from the bottom of the frame.

The upshot is that motion blur characteristics will be slightly different between cameras with electronic and mechanical shutters. To generalize, I guess you could say that at the same shutter speed an electronic shutter will tend to yield slighty less motion blur, and thus might be slightly sharper.

But these differences are very slight. In either case I would set the shutter to what is technically and aesthetically pleasing regardless of whatever format you're using.

As for high shutter speeds with electronic cameras, just do the math to figure out what the equivalent to 90 and 45 degree shutters, etc. At 24fps with a 180 degree shutter, you have an effective shutter speed of 1/48. At 90 degrees, the effective shutter speed is 1/100, at 45, 1/200, etc.

J
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#3 Brian Drysdale

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Posted 14 August 2006 - 10:04 AM

The upshot is that motion blur characteristics will be slightly different between cameras with electronic and mechanical shutters. To generalize, I guess you could say that at the same shutter speed an electronic shutter will tend to yield slighty less motion blur, and thus might be slightly sharper.


I had a conversation with a film editor friend about this. It centred on how the electronic shutter (when shooting progressive) seemed to be a bit more prone to giving a strobing effect during fast panning camera moves compared to the mechanical shutter used on film cameras.
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#4 John Ealer

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Posted 14 August 2006 - 10:18 AM

I had a conversation with a film editor friend about this. It centred on how the electronic shutter (when shooting progressive) seemed to be a bit more prone to giving a strobing effect during fast panning camera moves compared to the mechanical shutter used on film cameras.


Strobing is directly related to motion blur. The less motion blur, the more likely you are to perceive "strobing." Since, as we've discussed, the electronic shutter can tend to yield slightly less motion blur at the same shutter speed than a rotating mirror shutter, it follows that, all other things being equal, it might exhibit slightly greater "strobing" characteristics.

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#5 Brian Drysdale

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Posted 14 August 2006 - 10:39 AM

That's also the conclusion we came to.
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#6 Roberto Ditleff

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Posted 14 August 2006 - 12:50 PM

John
Thanks for the answers.

Are there any differences among the hd camera makes and models concerning the way their eletronic shutters work, I mean is there any hd camera that gives a better motion blur ?

TKS
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#7 John Ealer

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Posted 14 August 2006 - 12:56 PM

John
Thanks for the answers.

Are there any differences among the hd camera makes and models concerning the way their eletronic shutters work, I mean is there any hd camera that gives a better motion blur ?

TKS


I don't think you're going to find much functional difference between the way electronic shutters work. Almost all cameras have a "clear scan" or ECS feature which lets you dial in very specific shutter speeds in very small increments. You can use that feature to get a level of motion blur that you think is appropriate for your project.

J
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#8 David Mullen ASC

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Posted 14 August 2006 - 02:04 PM

Yes, there isn't really a difference between how 24P at 1/48th, for example, looks on one video camera versus another. It will be close to the look of a film shutter at 1/48th (180 degrees at 24 fps) but just not exactly the same. And then your choice is just to open up the shutter a little more (like to 1/32nd) and live with the increased blur & smear if you think 1/48th looks too strobey.

The only digital cameras with mechanical spinning mirror-reflex shutters are the Dalsa and Arri-D20.

The Viper has a very brief mechanical shutter, but that's just to clear the CCD charge. For anything close to 1/48th, you'd be using the electronic shutter.
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