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montwire
Joined: 13 Aug 2007
Posts: 7
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 Posted: Thu Jun 23, 2011 1:03 am Post subject: Does FPS Matter? |
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Do certain FPS work better that others a general rule?
Monty |
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Gorf
Joined: 10 Mar 2007
Posts: 111
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| Posted: Thu Jun 23, 2011 4:31 am Post subject: |
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No. FPS is irrelevant. In fact - it can cause problems with some 3D software that can't cope with non-integer framerates like 29.97fps.
Better to work with image sequences. |
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GraphicsKid
Joined: 25 May 2009
Posts: 480
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| Posted: Thu Jun 23, 2011 10:05 pm Post subject: |
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| It really only affects the playback speed. |
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scarabrae
Joined: 01 Jan 2010
Posts: 33
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| Posted: Sat Jun 25, 2011 6:16 am Post subject: |
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I was wondering about the fps that my canon 550D shoots at.
Is this what your asking, rather than PAL, NTSC or Film FPS?
Say I set my camera to record movies at 25fps...why would I then want to set my shutter speed to anything other that 1/25 of a second?
I understand about exposure, f-stops, etc when shooting stills and how this can effect my shot. I understand how I may want a shallow depth of field in my movie shots and a wide aperture may help then...and this may mean my shutter speed would increase to keep a decent exposure.
But.....what is the camera doing internally when I want it "output" my still image sequence at 25fps. Does it do some divisional math inside? Does it merge fraims together? Does it ultimately help "tracking" [rolling shutter aside] to set the sutter speed as fast as possible, while acknowledging the stills will be output at my chosen 25fps?
Hope this adds to and does not detract from your question, montwire.
Cheers |
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GraphicsKid
Joined: 25 May 2009
Posts: 480
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| Posted: Sat Jun 25, 2011 1:12 pm Post subject: |
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I'm not really sure what it is you're asking, but I'll take a stab at it here.
Shutter speed, when shooting ONLY affects the amount of motion blur and the amount of exposure. It doesn't make any difference to the frame rate. When shooting 25fps, a shutter speed of 1/25 is a 360 degree shutter... I don't think that's physically possible... or pretty. If you're going for a "filmlike" look, then use a 180 degree shutter... or 1/50 for 25 fps.
OR
Set the shutter as high as it will go so you can track the footage easier. Higher the shutter speed, the less motion blur you will have, and the clearer the track points will be. You can add the blur back in post... though sometimes that's a bit tricky getting it right.
Are you saying your camera will spit out STILLS at 25fps??? Or is it making a video at 25fps that you can extract the stills from later? |
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scarabrae
Joined: 01 Jan 2010
Posts: 33
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| Posted: Sat Jun 25, 2011 6:59 pm Post subject: |
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Hi
Its spitting out an H264 movie at 25 fps [if I set it to 25in the camera options] and I then use QT to say, make a targa sequence, again keeping to 25fps.
I think i'm getting my head around what your saying about 25 fps=shutter speed of 1/25 and therefore a 360 shutter.
Ill experiment with the same shot, with different shutter speeds but keeping a 25 fps output....cheers for clarifying this GraphicsKid |
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GraphicsKid
Joined: 25 May 2009
Posts: 480
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| Posted: Sun Jun 26, 2011 2:02 am Post subject: |
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If you're tracking it (which I'm sure you are, given that you're on the Syntheyes forums  ) it'll make your job easier if you use a high shutter speed so there's less blur. If it's a nice smooth and slow shot, then it shouldn't be a problem though. |
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Gorf
Joined: 10 Mar 2007
Posts: 111
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| Posted: Sun Jun 26, 2011 6:14 am Post subject: |
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| scarabrae wrote: | | I think i'm getting my head around what your saying about 25 fps=shutter speed of 1/25 and therefore a 360 shutter. |
No - 25fps does not mean the shutter speed is 1/25"
It just means the shutter speed can't be any slower than 1/25" (for example, you can't have the shutter open for 1/20")
The shutter speed is how long the shutter is "open" to let in light.
The frame rate is how many times per second a still image is photographed.
For any given frame, the shutter must have "closed" before the next frame is due to be photographed.
In bright sunlight, you will want a fast shutter, say 1/500". This means the shutter is "open" for 0.002 seconds. At 25fps, the time between this frame and the next is 1/25" or 0.04 seconds. So the shutter is "closed" for 0.038 seconds.
The words "open" and "closed" are in quotes because on modern equipment, there is no opaque barrier between the lens and the sensor - there's light always hitting the sensor, and a processor decides when to start collecting the light, and for how long. |
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scarabrae
Joined: 01 Jan 2010
Posts: 33
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| Posted: Sun Jun 26, 2011 9:19 am Post subject: |
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| Gorf wrote: | | scarabrae wrote: | | I think i'm getting my head around what your saying about 25 fps=shutter speed of 1/25 and therefore a 360 shutter. |
No - 25fps does not mean the shutter speed is 1/25"
It just means the shutter speed can't be any slower than 1/25" (for example, you can't have the shutter open for 1/20")
The shutter speed is how long the shutter is "open" to let in light.
The frame rate is how many times per second a still image is photographed.
For any given frame, the shutter must have "closed" before the next frame is due to be photographed.
In bright sunlight, you will want a fast shutter, say 1/500". This means the shutter is "open" for 0.002 seconds. At 25fps, the time between this frame and the next is 1/25" or 0.04 seconds. So the shutter is "closed" for 0.038 seconds.
The words "open" and "closed" are in quotes because on modern equipment, there is no opaque barrier between the lens and the sensor - there's light always hitting the sensor, and a processor decides when to start collecting the light, and for how long. |
Thanks for this expalantion... |
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FloridaJo
Joined: 29 Aug 2010
Posts: 29
Location: Venice, FL
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| Posted: Sun Jun 26, 2011 10:56 pm Post subject: |
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Actually shutter speed should be 2x the denominator of the FPS.
ie, 24 fps 1/50 or faster; 30 fps, 1/60 or faster. |
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GraphicsKid
Joined: 25 May 2009
Posts: 480
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| Posted: Mon Jun 27, 2011 12:57 am Post subject: |
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| FloridaJo wrote: | Actually shutter speed should be 2x the denominator of the FPS.
ie, 24 fps 1/50 or faster; 30 fps, 1/60 or faster. |
What do you mean "should"? You can have a longer shutter than just 180 degrees... The new "The Hobbit" films are being shot at 48 fps with a 270 degree shutter. That means a 1/64 shutter speed, which is greater than the 1/96 shutter speed you're suggesting. |
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FloridaJo
Joined: 29 Aug 2010
Posts: 29
Location: Venice, FL
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| Posted: Mon Jun 27, 2011 5:36 am Post subject: |
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| I'm talking digital, you're talking film. |
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Gorf
Joined: 10 Mar 2007
Posts: 111
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| Posted: Mon Jun 27, 2011 5:53 am Post subject: |
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| FloridaJo wrote: | | I'm talking digital, you're talking film. |
And everyone knows, you can't track footage if it was originally shot on film. Peter Jackson is having to genetically engineer a real Smaug because he can't add a matchmoved dragon in post.
It's true - why do you think there have been so many delays? It's not easy. He started off with a croc, a bat and a flamethrower and ended up with a blind creature that loved nocturnal carrion barbecues. |
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Gorf
Joined: 10 Mar 2007
Posts: 111
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| Posted: Mon Jun 27, 2011 6:15 am Post subject: |
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| FloridaJo wrote: | | I'm talking digital, you're talking film. |
After the briefest of searches, it turns out you're actually talking rubbish.
RED cameras are digital and go as slow as 1/24" - a 360 degree shutter!
Wonder if there's any use for it... |
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FloridaJo
Joined: 29 Aug 2010
Posts: 29
Location: Venice, FL
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| Posted: Mon Jun 27, 2011 6:38 am Post subject: |
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| There's no mechanical shutter in digital. |
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