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reply to david mullen sir


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#1 ramesh bhatnagar

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Posted 25 January 2009 - 04:56 AM

thank u divid mullen sir, i write my real name. ramesh bhatnagar " ramy". sir what i learn here that is we used shutter as door . which allowed light to fell on film. after we set our aperture. and used aperture no. for dept of field. but my sir said that shutter is only for used as door this has no relation about blur. as i say when we catch fast moving object we keep fast shutter speed for still camera. but my sir said we capture moving object with controlling fps for ig. for fighter plane we keep more then 200 fps. rather then 24fps. he said we are playing with fps in moving object. not with shutter angle . but my another friend said we keep shtter speed for moving object to get sharpe and clean and no blur. that why im confused. so sir can you explain me that please. thanks sir unsure.gif
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#2 Stephen Williams

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Posted 25 January 2009 - 05:08 AM

If you reduce the size of the shutter (door) to 90 degrees or 45 degrees, the image will be sharper. Remember to open the iris 1 or 2 stops to compensate. BTW not all cameras have an adjustable shutter.

thank u divid mullen sir, i write my real name. ramesh bhatnagar " ramy". sir what i learn here that is we used shutter as door . which allowed light to fell on film. after we set our aperture. and used aperture no. for dept of field. but my sir said that shutter is only for used as door this has no relation about blur. as i say when we catch fast moving object we keep fast shutter speed for still camera. but my sir said we capture moving object with controlling fps for ig. for fighter plane we keep more then 200 fps. rather then 24fps. he said we are playing with fps in moving object. not with shutter angle . but my another friend said we keep shtter speed for moving object to get sharpe and clean and no blur. that why im confused. so sir can you explain me that please. thanks sir unsure.gif


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#3 David Mullen ASC

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Posted 25 January 2009 - 10:48 AM

Shutter speed (exposure time) controls the amount of motion blur a moving object creates in the frame, and shutter speed is the result of the frame rate + shutter angle.

So at high frames, the shutter speed is naturally shorter because, if the shutter angle is 180 degrees, then at (let's say) 100 fps, the shutter speed becomes 1/200th of a second. So at high frames there are both more motion samples and less exposure time, so less blur per frame.

Some people, when shooting normal speed but plan on slowing down the footage in post, will close down the shutter angle (or in a video camera, use a faster shutter time) to reduce the amount of per-frame blur so that when they start repeating frames in post, the amount of motion blur is similar to what would happen by shooting a higher frame rates. However, in this case, they don't have as many motion samples to work with in post so the slowed-down motion is "steppy."
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#4 Jim Hyslop

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Posted 25 January 2009 - 10:51 PM

but my sir said that shutter is only for used as door this has no relation about blur. as i say when we catch fast moving object we keep fast shutter speed for still camera. but my sir said we capture moving object with controlling fps for ig. for fighter plane we keep more then 200 fps. rather then 24fps.


Your instructor is only partly right (or perhaps you have misunderstood him). Yes, the shutter is a door, but that door does have a direct effect on blur. The longer you hold the door open, the more blur there will be. To reduce blur, you need to reduce the amount of time the door is open (i.e. increase the shutter speed).

As David Mullen points out, shutter speed is a function of both shutter angle and frame rate. The formula is quite simple:
shutter angle
shutter speed = ------------------
				 360 x frame rate

Therefore, there are two ways to increase shutter speed, and thereby reduce blur: increase the frame rate (which seems to be what your friend and your instructor are both saying), or to decrease the shutter angle.

Assuming a shutter angle of 180 degrees, 200fps will result in a shutter speed of 1/400 second, which will certainly reduce or even eliminate blur. However, since you are running the film through the camera approximately 8 times faster than normal, it will also result in extreme slow motion - an object which would take one second to cross the frame while filming, will take approximately 8 seconds when projected. You may not necessarily want that effect. You should be able to return the shot to normal speed in post, by printing every 8th frame.

Shooting the same subject at 24fps, but reducing the shutter angle to 22 degrees, will also result in a shutter speed of 1/400 second.

As Stephen has pointed out, not all cameras have an adjustable shutter. If yours doesn't, then you'll have to figure out which is cheaper for those shots - renting a camera with an adjustable shutter, or shooting 8 times as much film and any extra post production expenses.

--
Jim
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#5 ramesh bhatnagar

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Posted 26 January 2009 - 11:18 AM

thank you david sir, thanks you Stephen William sir, thanks you Jim sir, thanks all of you....you r men...
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