Differences Between Shutter and FPS at DVinfo.net

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Canon XL and GL Series DV Camcorders
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Old February 14th, 2005, 09:48 PM   #1
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Differences Between Shutter and FPS

if you have 24p. Why is it 48 on shutter speed or 125. That does shutter speed do. Isnt it how many pictures it takes in a second and puts it on Your frames or something like that?
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Old February 14th, 2005, 10:15 PM   #2
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It's basically the shutter speed, but it's not affecting the frame rate. It's the electronic equivalent to changing the shutter angle on a film camera. It's still running at 24 frames per second but the exposure time is shortened, if you go to 1/60th, or lengthened if you go to 1/24th.

If you are in a low light situation, you can sometimes get away with going to 1/24th shutter speed and get an extra stop of light. This is good, because then you don't have to use the gain, or use as much gain.
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Old February 15th, 2005, 12:55 AM   #3
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The frame rate is the number of frames per second that get exposed.

The shutter speed is the amount of time that each frame gets exposed.

The XL2 is capable of shooting at three different frame rates: 24, 30, and 60 (24 and 30 are full progressive-scan frames, 60 is for half-resolution fields).

However, for any of those frame rates, you can choose from a wide variety of shutter speeds. Slower shutter speeds (like 1/24) let in more light, and cause more blur, than faster shutter speeds (like 1/125, 1/500, etc).

If you're shooting in 24p, then no matter what shutter speed you select, the camera will image 24 discrete frames per second.

Usually, to simulate a film camera with a 180-degree shutter, you would use 1/48 for the shutter speed in 24p, and 1/60 for the shutter speed in 30p.
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Old February 15th, 2005, 04:11 AM   #4
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I've often heard it recommended to use 1/50th of a second when filming 25p and have not really understood this.

The default for the XL2 is 1/25th of a second so that the frame rate and shutter speed are in sync. I assume that the faster the shutter speed the less time each frame is exposed and thus the greater the time between the exposure of each frame. I would expect then that the faster the shutter speed the less blurred and hence more jerky motion would appear.

Thus why is it not better to film 1/25th of a second at 25p?

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Geoff
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Old February 15th, 2005, 11:17 AM   #5
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Because of the previously stated motion blur problem. You would be exposing your images a little too much and fast motion might look bad.
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Old February 15th, 2005, 06:59 PM   #6
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At 1/50, your footage will indeed appear more "jerky" -- but it'll also exactly match the motion of film shot at 25fps on a movie camera with a 180-degree shutter.

At 1/25, the motion will be substantially more blurred, and not film-like. 1/50 gives you the look and motion rendition of film.
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Old February 16th, 2005, 06:22 AM   #7
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So this is for a purely aesthetic reason (i.e. to simulate the look of film)? There are no technical reasons (for instance if one was wanting to do a film transfer later) why it is desirable to shoot 1/50th of a second for 25p.

I had a quick look at the Swiss Effects website and they specify not to exceed 1/50th of a second ( they say: "as differences in field sharpness affect the quality of the field interpolation during transfer") but do not say anything about a lower limit on shutter speed.

Regards,

Geoff
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