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shutter speed

Jaysingh rajpurohit

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Usage often depends on how you set up the exposure time on a particular camera. On film cameras you usually adjust the shutter angle (180 degrees commonly being the normal setting), while digital cameras they tend to set up the shutter speed (although some have either option). The principle is explained here:




BTW It would be better to ask the technical questions in another part of the forum, since this section is about cinematographers and their work, rather than technical questions.

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Okay, I was already typing this up, so I'll go ahead post it:


To put it in simplest terms, in motion picture cameras, the shutter

generally takes the form of a rotating disc with a wedge cut out of it,

like a pie with a missing slice. The open wedge is the part that allows

light to reach the film.


The term "shutter angle" refers to the angular sweep of the open wedge.

So, a 180 degree shutter angle would be half of the total disc.

A 90 degree shutter angle would be one-quarter of the total disc, and so on.


Some cameras have a fixed shutter angle, while others have variable shutter angles.


Shutter angle is one of the factors that determines shutter speed.

The other factor is the speed at which the shutter rotates.


At 24 frames per second, the shutter makes one complete revolution every

24th of a second. If our shutter angle is 180 degrees, then for exactly

one-half of that time the shutter will expose the film, that is, the

shutter speed will be 1/48th of a second.


Here's the formula:


Exposure time (or shutter speed) = (Shutter angle/360) X (1/frames per second)



Wide shutter angles naturally provide longer exposure times, while narrow

shutter angles have shorter exposure times.


Besides controlling the amount of light, the shutter angle will also affect

the amount of blur a moving subject records on the film. Wide angles allow

more blur; narrow angles allow less blur.

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Adding to the above, film cameras with variable shutters rarely go wider than 180 degrees because of the reason the shutter is there in the first place: It protects the film from exposure during the mechanical pulldown from one frame to the next. Angles as large as 288 degrees have been used with specially designed film movements (the hot kinescope process of the 1950's). With digital cameras, you can get shutter angles within just a hair of a full 360 degrees. This enables some interesting possibilities. With that much motion blur you're immune from skipping (aka incorrectly "strobing").





-- J.S.

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