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what determines amount of motion blur??


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#1 sam williams

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Posted 09 October 2008 - 11:27 AM

hi,

i was curious as to how i can figure out how much motion blur will be picked up by a certain camera setting. Im quite new to cinematography and i will be filming a dance video soon and i want to make sure i dont set the camera incorrectly so there is loads of motion blur. Is there at all a way of fine tuning how much motion blur you will get when setting up the camera, i think its something to do with shutter speed and exposure??? but im not sure

could someone please enlighten my poor old brain - by the way i am using the sdx 900.


thanks,

sam
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#2 Scott Fritzshall

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Posted 09 October 2008 - 12:13 PM

Motion blur is a function of how long the shutter is open for. If you've got it open for a long time, like in time lapse photographs, you get a lot of motion blur, and if you've got it open for a very short period of time, you get very little motion blur. For film, you typically have a 180deg shutter, and run the camera at 24fps. This means that each frame is exposed for 1/48 of a second. If you ran the camera at 48fps, you would expose each frame for 1/96 of a second, and so on. If you ran the camera at 24fps but closed the shutter to 90deg, you would again expose each frame for 1/96 of a second, and get half as much motion blur as you would have with a 180deg shutter. Exposure is related here because if you close the shutter or change the framerate, you change how long the film is exposed for, and thus must compensate by adjusting light levels or f-stop. In the previous examples, because you expose the film for half as long, you compensate by adding 1 stop of additional light.

On a video camera, if you're trying to emulate the motion signature of film, you want 24 frames per second and a shutter speed of 1/48. I think some consumer cameras try to make themselves more sensitive by just having no shutter and exposing for the entire frame duration, which doubles motion blur and in my opinion makes everything unpleasantly smooth.
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#3 John Sprung

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Posted 10 October 2008 - 05:40 PM

... i want to make sure i dont set the camera incorrectly so there is loads of motion blur.

You also want to take care not to have too little motion blur. Without motion blur, there is no illusion of motion, and your film looks like a very rapid sequence of still frames.

Since you're shooting on video, you can do an instant test. Pick your frame rate and exposure time, shoot some motion, do some pans, and look at it. Try a few combinations and see what you like. When you've decided, just rewind and record over your tests.




-- J.S.
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#4 sam williams

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Posted 12 October 2008 - 03:35 AM

thanks for your help guys
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#5 David Mullen ASC

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Posted 12 October 2008 - 11:27 AM

In combination with the shutter time, motion blur also determined by how fast the subject or camera is moving (obviously.) You could use a 360 degree shutter (i.e. no shutter) and if nothing is moving in the frame, or barely moving, you are not going to notice anything unusual in terms of blur.
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