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I am trying to do forensic analysis on a film which was recorded in the early 1970's. I don't know what kind of film was used or what type of camera, except that it was 8 mm format.
Does anyone know what the shutter speed would likely be for an outdoor sun lit clear blue day? Also, is there a standard for the shutter geometry? Is it likely to be a sliding door that closes from top to bottom, right to left, etc?
Any help would be greatly appreciated from the knowledgable folks here.
Thanks!
I'm not the most knowledgeable one on this forum to answer this, but I'd guess there's no accurate way to know this without knowing what camera shot the footage.
Matt Pacini
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THere are two different shutter construction around:
The most simple one is a rotating disc with an open sector. The disk is rotating between lens and film surface. Every time, when the open sector passes the lens, the light beats onto the film surface. The amount of light depends on the opening angle of the sector and on the rotation speed (framerate). During the closed part of the disc, the film is forwarded to the next frame.
Usual opening angles in that time had been 160...180 degree. That means, that at 18 fps as S8 standard framerate for home movies, each frame is exposured with 1/36 sec. A realistic iris setting for that exposure time would be 5,6...11, depending on overall camera construction, beam divider prism ratio, film speed 40 ASA with conversion filter and so on.
Another type of shutter is the Beaulieu shutter, which performes a sliding door in vertical direction. THe shutter is adjustable, the gap of the door can be reduced until it?s totally closed and the exposure time in infinity short. In normal position, that shutter performs about 1/72 sec at 24 fps or in low light position 1/60 sec at 24 fps.
As this camera constructions don?t use a beam divider for the viewfinder, a huge amount of light rests for the exposure, so that the iris on a sunny day would close to about stop 11. (40 ASA with conversion filter).
Pedro
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<BLOCKQUOTE><font size="1" face="Courier, Arial">quote:</font><HR>Originally posted by muritai:
And the rotating disk would allow fast moving images that were the farthest from the axis of rotation of the radial shutter to blur more.
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The blades are usually angled to, more or less, be level as they swing across the gate. So there really would not be a difference between one edge and the other. Where the WILL be a difference is if the action of the subject is moving in the same direction as the movement of the shutter. If an object is moving the opposite direction as the shutter, then that object will come out sharper than if it is moving in the same direction as the shutter, in which case it will blur more as the shutter "chases" it. Speed and shutter opening size also plays a part in that formula, as well. An interesting thing to do is shoot someone jumping on a trampoline and try different shutter angles. With certain combinations, they will be sharp as a tack going one direction and blurred as can be going the opposite direction.
Girls on trampolines? Good subject to test this on..... "The Super 8 Man Show". http://www.hostboard.com/ubb/wink.gif
Roger
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Roger Evans
MovieStuff
http://www.afterimagephoto.tv/moviestuff.html
What I am trying to do analysis on is a rotating blade, which, of course is moving faster than the frame rate.
Is there a way to tell which mechanical shutter scheme the camera is using by looking at the manner in which fast moving objects blur in the screen?
It seems that the shutter (if it moves up and down, rather than right and left) would let fast moving images in the top of the view (or bottom, depending on whether the shutter comes from the bottom or the top) to blur more.
And the rotating disk would allow fast moving images that were the farthest from the axis of rotation of the radial shutter to blur more.
Does that seem reasonable?
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