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Old March 4th, 2009, 10:36 AM   #1
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Progressive, shutter speed & frames rate.

Greetings.

I've been reading about the advantages of progressive shooting. One comment that keeps coming up is that progressive shows blur and camera movement should be slow and smooth.

So here's my question coming from a still photography background:

If I'm shooting 30p (on Canon HV30) I understand that that is shooting 30 frames per second. So my thinking is that I need to set the camera shutter speed at anything faster than 1/30th second, though a 30th could work in some situations where movement is minimal.

In still, if you shoot something moving at 1/30th of a second, that moving subject will appear blurred.

Since my video camera has shutter speeds that go up to 2000th second, wouldn't shooting at something like at least a 125th, 250th, or 500th second solve all the problems that might be associated with the blurring issues associated with 30p, or any video mode for that fact?

Obviously, I'm aware that there must be enough light so that thee aperture can be be opened according to the setting of the shutter speed.

Am I barking up the right tree? I think Bill Pryor is gonna kill me if he sees one more post about this. But if my hypothesis above is correct, then I completely understand.

Thanks.

Jonathan
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Old March 4th, 2009, 12:35 PM   #2
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The blurring helps smooth movement - the usual shutter speeds at 30p is 1/60th sec, so there will be some blurring on movement.

I suspect this high shutter speed idea is a carry over from stills photography and is best dropped in video or motion picture photography unless you want a visual effect. Video and film works as a progression of frames, so what each individual frame looks like is of no importance unless you're doing a freeze frame. It's how the image looks when screened the correct frame rate that matters.

Having the blurring is an important element in each frame during action to help the eye carry the movement over to the next frame. With the higher shutter speed movement becomes much more strobby, rather than smooth. An example of this is "Saving Private Ryan", where a higher shutter speed was used to create the look of some wartime newsreel cameras.
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Old March 4th, 2009, 03:31 PM   #3
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Brian,

Thanks for explaining that. I can see your point about have some blur to blend frame to frame. I think I'm clear now on the "stroby" effect you mention, and the Private Ryan example was great, especially since I've seen that movie many times.

Here is another hypothetical question:

At the other end of the spectrum, lets say I shot at a slower shutter speed i.e 1/15th second, 1/8th second and so on. What effect might that have, andis there some movie I may have seen that in?

My limited knowledge tells me that this wouldn't even work since the video is advancing at 30fps, the fact that it would take each frame to expose wouldn't match up. So me thinks that there would be frames that would just be cut off mid exposure.

What I'm gathering is that the safest thing to do is to shoot at either 1/30th or 1/60 second at a frame rate of 30fps.

Thanks again.

Jonathan
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Old March 4th, 2009, 03:36 PM   #4
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With slow motion shot with a high frame rate, I personally don't find the frame blurring to be as important since slo-mo footage is not jarring like real time footage can be. If you're slowing down footage that was shot at real time, the strobing effect will be somewhat inevitable.
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Old March 4th, 2009, 04:22 PM   #5
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Quote:
Originally Posted by Kent Frost View Post
With slow motion shot with a high frame rate, I personally don't find the frame blurring to be as important since slo-mo footage is not jarring like real time footage can be. If you're slowing down footage that was shot at real time, the strobing effect will be somewhat inevitable.
The shutter speed automatically increases as you increase the in camera frame rate. A higher shutter speed that matches this when creating a slow motion effect in post works well. In some slow motion work synced strobe lighting is used to create a very "crisp" edged effect as used in breakfast cereal & drinks commercials, especially when the product is being poured.
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Old March 4th, 2009, 04:59 PM   #6
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30 FPS- __________ __________ __________ __________ __________ __________

Shut. spd _____ _____ _____ _____ _____ _____
1/60th

Does this diagram make sense? Top line is the conituous FPS, in this case 30.

Bottom line is the exposure shutter speed for each frame, in this case 1/60th second.

In my diagram, IF the shutter speed was 1/30th sec, the lines on the shutter speed would be the same lenghth as the top FPS(30).

Is this correct?

I'm done.

Thanks again fellas.

Jonathan

Jonathan

Last edited by Jonathan Levin; March 4th, 2009 at 05:00 PM. Reason: format problem
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Old March 4th, 2009, 05:04 PM   #7
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Sorry about the above post. The left side of the shutter speed lines should each match up with the left side of the fps lines above. The web reformated me. Hopefully you get the idea.
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Old March 4th, 2009, 06:32 PM   #8
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1/60th of a second shutter does not mean that it fires 60 times in a second. For each of the 30 frames in a clip that is shot at 30fps, the shutter fires one time per frame, but at a length of 1/60th of a second. So there's still only 1 image per frame, but the length of the exposure is 1/60th.
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Old March 4th, 2009, 06:46 PM   #9
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Here's a visual aid:

http://www.djspiral.com/images/misc/10frames.GIF

The link above is an image of a composite of 10 consecutive frames of video shot at 30fps with a 1/30th sec shutter speed. The subject is a person at night swinging glowsticks on the end of strings.

As you can see, there is a fine break between each frame. Had I shot this at 1/60th sec, the breaks between the frames would be twice as thick.
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Old March 4th, 2009, 07:40 PM   #10
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Kent,

Thanks for the teaching aid! I think what I was trying to illustrate in my above post is exactly what you are trying patiently to explain. Because of the format issue, my diagram makes it appear that there is more than one shutter exposure per frame, which was not my intention.

MAybe I'll redo that in photoshop quick.

Thanks for your replies.

Jonathan
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Old March 4th, 2009, 08:04 PM   #11
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Ok. Here is my chart as I had originally intended:
Attached Thumbnails
Progressive, shutter speed & frames rate.-fps-chart.jpg  
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Old March 4th, 2009, 08:06 PM   #12
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Yep, that looks about right! :D
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Old March 7th, 2009, 04:59 PM   #13
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Quote:
Originally Posted by Jonathan Levin View Post
Here is another hypothetical question:

At the other end of the spectrum, lets say I shot at a slower shutter speed i.e 1/15th second, 1/8th second and so on. What effect might that have, andis there some movie I may have seen that in?

My limited knowledge tells me that this wouldn't even work since the video is advancing at 30fps, the fact that it would take each frame to expose wouldn't match up. So me thinks that there would be frames that would just be cut off mid exposure.
No, the way to imagine the situation is to think of a series of long exposure frames lasting (say) 1/4 second each, but with the start and end of consecutive frames moved forward in time by the frame rate. Obviously there will be a lot of frames which overlap each other in time. Nett result will be stationary scenes look normal, but movement looks blurry, objects leaving a ghostly trail, for want of a better description..

Practically, may be useful for dream like sequences, and something similar I seem to remember in the X-files opening sequence, though it may be better to get the effect in post. It will also have the effect of improving the exposure in low light conditions - may be useful when there's very little motion in a shot. (Or when a dream like sequence is wanted when the lightings dim! :-) )
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