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film sensitivity, apeture and shutter speed help...


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#1 sam williams

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Posted 03 October 2008 - 06:58 PM

hello,

im not sure im understanding this correctly.

why are all three of these variables necessary - shutter speed, aperture and varieties of film sensitivities, surely they are all effecting the same aspect of recording an image, by reducing or increasing the amount of light that is recorded on the film or ccd.

When you increase the size of the aperture, the shutter speed must increase. When you have a very long shutter speed, the aperture must be very small to avoid over exposure, and likewise, the sensitivity of the film stock or iso value must be considered depending on how much light is to be let into the camera. Surely if they are all compensating for each other, there is no need for variations in all three of these features. Cant just one of these things be adjustable depending on the kind of shot you want to take?

i kind of know im wrong, but i just wanted a concise answer so i could finally understand the need for each of these attributes.


thanks,

sam
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#2 John Brawley

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Posted 04 October 2008 - 03:17 AM

i kind of know im wrong, but i just wanted a concise answer so i could finally understand the need for each of these attributes.


Hello Sam.

They are all ways of controlling the exposure, but they all have *side effects* that affect other parts of the image making process, that are desirable or perhaps even not desirable.

Aperture affects how much of the image is "in" focus and "out" of focus.
Shutter speed affects how "sharp" the image appears to be.
Film ISO affects how grainy or grainless the image is.

They all control how the image is exposed but each also has it's unique set of characteristics that allow a creative cinematographer to manipulate the visual outcome.

jb
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#3 David Mullen ASC

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Posted 04 October 2008 - 05:18 AM

Or to put it another way, aperture affects depth of field, shutter affects motion blur, and different speed film stocks have different grain levels.

Generally when shooting film, you stick to a standard 180 degree shutter angle and use aperture and/or ND filters to control exposure. You only adjust the shutter angle to either change the motion blur characteristics (to get choppier, more staccato motion in action scenes for example) or to sync with certain pulsing light sources.
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#4 sam williams

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Posted 05 October 2008 - 04:40 PM

thanks for your time guys,

sam
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Glidecam

Metropolis Post

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Willys Widgets

Visual Products

rebotnix Technologies

FJS International, LLC

Rig Wheels Passport

Gamma Ray Digital Inc

Media Blackout - Custom Cables and AKS

Paralinx LLC