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using the light meter


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#1 wilfred louis

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Posted 14 September 2009 - 05:51 AM

Hi,

I will be shooting in super 16mm and I have a Minolta V meter. I plan to shoot at 24 fps at 180 shutter angle. I am a bit confused. The AC manual talks of the shutter travelling a speed of 1/48 of sec. What does this mean? and when I take a reading should I meter at 24?
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#2 Tom Jensen

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Posted 14 September 2009 - 08:49 AM

Hi,

I will be shooting in super 16mm and I have a Minolta V meter. I plan to shoot at 24 fps at 180 shutter angle. I am a bit confused. The AC manual talks of the shutter travelling a speed of 1/48 of sec. What does this mean? and when I take a reading should I meter at 24?


At 24 fps a shutter makes 24 complete rotations every second. The shutter is a semi circle so as the shutter spins the film is only being exposed half the time. Each complete frame is 1/24th of a second and half of that is 1/48th of a second.
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#3 wilfred louis

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Posted 15 September 2009 - 04:28 AM

At 24 fps a shutter makes 24 complete rotations every second. The shutter is a semi circle so as the shutter spins the film is only being exposed half the time. Each complete frame is 1/24th of a second and half of that is 1/48th of a second.


Thanks Tom...so on The left of my light meter screen I should I set it to 24fps or 48fps...but come to think of it there is no 48...it goes from 32 to 64...sorry all this may sound a bit dumb but I am confused since I have that still photography mind set.
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#4 Adrian Sierkowski

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Posted 15 September 2009 - 05:23 AM

Meter should be set to 24Fps and most of them assume the 1/48th of a second already (or rather in "cine mode" they assume a 180 degree shutter and do the math for you)
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#5 Rob Vogt

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Posted 15 September 2009 - 08:16 AM

The reason is because 180 degrees is half of 360, the full circle. That means that your shutter exposes film every 1/48th of a second because half the time the shutter is open letting light in, and the other half it is closed allowing the film to advance to the next frame in the gate.
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#6 wilfred louis

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Posted 16 September 2009 - 02:17 AM

Meter should be set to 24Fps and most of them assume the 1/48th of a second already (or rather in "cine mode" they assume a 180 degree shutter and do the math for you)


Got it...Thanks Adrian. Now if I am using an DSLR to check my shot then what shutter speed should I set the DSLR to? I am assuming it should be 1/48 and NOT 1/24...am I right? (my Canon 400D has shutter speeds of 1/25 and 1/50)
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#7 wilfred louis

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Posted 16 September 2009 - 02:32 AM

The reason is because 180 degrees is half of 360, the full circle. That means that your shutter exposes film every 1/48th of a second because half the time the shutter is open letting light in, and the other half it is closed allowing the film to advance to the next frame in the gate.


Thanks Rob...another question that is bothering me is that when... 'the other half is closed allowing the film to advance to the next frame in the gate'...once the film is developed why DONT we see a whole black frame between each exposed frame...all we see is a thin black strip between each exposed frame. Is this something to do with the film perf or some internal mechanism in the camera that moves the film just that much when the shutter is closed?
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#8 Rob Vogt

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Posted 16 September 2009 - 07:59 AM

thats correct. The film is not continuously moving. It is advanced, it stops to get exposed then the shutter closes and advances the film. If you've ever taken a photograph with a long exposure and moved, you'd see the image gets all blurry, if the film was moving while being exposed you'd get a similar result to that.
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#9 Jim Hyslop

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Posted 16 September 2009 - 09:38 PM

Thanks Rob...another question that is bothering me is that when... 'the other half is closed allowing the film to advance to the next frame in the gate'...once the film is developed why DONT we see a whole black frame between each exposed frame...all we see is a thin black strip between each exposed frame. Is this something to do with the film perf or some internal mechanism in the camera that moves the film just that much when the shutter is closed?

You mentioned earlier a still photography background. Assuming you meant with film, then it's exactly like shooting multiple shots with a motor drive (can you tell I'm old enough that my first SLR was manually advanced? :-) - the film advances, stops, the shutter opens then closes, the film advances, etc. etc.

--
Jim
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#10 Tom Jensen

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Posted 16 September 2009 - 10:56 PM

1/50th of a second is close enough. As the film advance and the picture is visible to the eye a picture is being taken. When the 180 degree shutter is not in the viewing system, mechanical claws in the movement are pulling down on the film and advancing the frame. Once it advances, steel pins within the movement are holding that frame perfectly still for 1/48th of a second and the picture is taken. The process is repeated 24 times per second. If a camera is shooting at 120 frames per second it is doing this 120 times per second. It really is amazing. If you project it back at 24 frames per second you will have slow motion. Also the flicker that you see is the shutter rotating. Half the time you see the image and the other half you see black. When light hits the lens, it bounces off the mirror and into your eyepiece. When it moves out of the way, the light hits the film.
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#11 wilfred louis

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Posted 17 September 2009 - 12:50 AM

1/50th of a second is close enough. As the film advance and the picture is visible to the eye a picture is being taken. When the 180 degree shutter is not in the viewing system, mechanical claws in the movement are pulling down on the film and advancing the frame. Once it advances, steel pins within the movement are holding that frame perfectly still for 1/48th of a second and the picture is taken. The process is repeated 24 times per second. If a camera is shooting at 120 frames per second it is doing this 120 times per second. It really is amazing. If you project it back at 24 frames per second you will have slow motion. Also the flicker that you see is the shutter rotating. Half the time you see the image and the other half you see black. When light hits the lens, it bounces off the mirror and into your eyepiece. When it moves out of the way, the light hits the film.




Thanks Tom, Adrian, Rob & Jim...I really appreciate the help...see you the next time film flummoxes me...Thanks once again...
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#12 nareshkancharana

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Posted 14 October 2009 - 12:21 AM

Thanks Rob...another question that is bothering me is that when... 'the other half is closed allowing the film to advance to the next frame in the gate'...once the film is developed why DONT we see a whole black frame between each exposed frame...all we see is a thin black strip between each exposed frame. Is this something to do with the film perf or some internal mechanism in the camera that moves the film just that much when the shutter is closed?


no man,at first the frame is exposed and after the rotating shutter moves the exposed frame down and new frame came
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#13 Chris Millar

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Posted 14 October 2009 - 03:08 AM

That means that your shutter exposes film every 1/48th of a second because half the time the shutter is open letting light in, and the other half it is closed allowing the film to advance to the next frame in the gate.


:huh:

It exposes for 1/48 sec every 1/24th of a second - not every 1/48th
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