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Determining Exposure time


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#1 kyle ragaller

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Posted 09 March 2008 - 11:15 AM

I have a Canon 1218 Autozoom that has a shutter angle of 165 degrees. Now, I know the simple equation to determine exposure time for any give frame rate but am having trouble getting a workable answer (I get 11/640 or something like that). I recently had a lecture on the subject of exposure time but didn't quite grasp onto the importance of knowing the exposure time. I do understand that depending on the change in frame rate a change also has to be made along your f/stops to keep a steady exposure. Is that all thats needed to know in association to exposure time (if the speed is increased or decreased you have to close down or open up by a stop or two to compensate)?

My shutter angle is 165 degrees and I have the settings of 18fps, 24fps, and slow mo (either 45 or 53fps, had conflicting sources on "slow mo" speeds). That reminds me, does anyone know what Canon's slow mo setting is for an old camera like mine? Super8wiki had a number from the manual then another from Canon's Museum.
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#2 David Mullen ASC

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Posted 09 March 2008 - 11:40 AM

Shutter speed would be something like:
1 / (frame rate) x 360/shutter angle

So 360 / 165 = 2.18

At 18 fps, the shutter speed would be 1/39
At 24 fps, the shutter speed would be 1/52
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#3 kyle ragaller

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Posted 09 March 2008 - 03:07 PM

Shutter speed would be something like:
1 / (frame rate) x 360/shutter angle

So 360 / 165 = 2.18

At 18 fps, the shutter speed would be 1/39
At 24 fps, the shutter speed would be 1/52


Thanks, I was told that the equation was 1/fps x shutter angle/360. Maybe the professor was confused, but this clarification helps. Thanks.

I am still wondering if anyone knows what the frame rate of Canon's slow mo is because it might come in handy to know. Thanks.
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#4 David Mullen ASC

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Posted 09 March 2008 - 04:46 PM

Thanks, I was told that the equation was 1/fps x shutter angle/360.


That's the same equation -- mine just had the 1/ covering over everything. Your professor's equation is probably better.

1
24 fps x 2 (which is 360/180) =

1/48

or

1/24 x 1/2 (which is 180/360) =

1/48
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