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200 degree shutter


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#1 Gian Claudio

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Posted 06 September 2009 - 09:42 AM

How does the 200 degree shutter aperture (i. e. in Platinum and GII cameras) work without exposing the film transport phase? Is the film transport phase "faster" than the exposing moment? To be more explicit: how long does it take, assuming we are shooting 24fps , to the threading mechanism to move down the film of 4 perfs, before it can expose the next steady frame? Why is this not possible in Arri cameras? Is it related in any way to the different nature of the shutters (single blade vs dual blade or film plane positioning vs 45° inclination)?
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#2 Stephen Williams

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Posted 06 September 2009 - 12:08 PM

How does the 200 degree shutter aperture (i. e. in Platinum and GII cameras) work without exposing the film transport phase? Is the film transport phase "faster" than the exposing moment? To be more explicit: how long does it take, assuming we are shooting 24fps , to the threading mechanism to move down the film of 4 perfs, before it can expose the next steady frame? Why is this not possible in Arri cameras? Is it related in any way to the different nature of the shutters (single blade vs dual blade or film plane positioning vs 45° inclination)?


Hi,

The film advance happens during 160 degrees, being normal & not high speed cameras it's possible, so yes the film advance is slightly faster. Down side is the shutter can not be fully closed. Arri never incorporated it & PV seem to have dropped the 'feature'.

Stephen
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#3 Tim Carroll

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Posted 09 September 2009 - 08:19 AM

Hi,

The film advance happens during 160 degrees, being normal & not high speed cameras it's possible, so yes the film advance is slightly faster. Down side is the shutter can not be fully closed. Arri never incorporated it & PV seem to have dropped the 'feature'.

Stephen


If my sources are correct, ARRI did incorporate a 200º shutter in their 2-Perf Arriflex 35 IIC cameras. Of course, with that camera you are only moving the film down two perfs during each frame advance, so the 160º gives enough time to cover it.

Best,
-Tim
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#4 John Sprung

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Posted 09 September 2009 - 03:43 PM

It's pretty much all in the design of the cams. The first Arri, the Model I, used a simple eccentric screw to drive the claw vertically, and required a 120 degree shutter. When they went to the cardioid cam, they were able to make it "dwell" at the top and bottom of the stroke, which allowed them to go to 180 degrees. Widen the fat side of the cam a little more, and you can do 200 degrees.

To get something really big, like the 288 degree shutter of the Acme kinescope camera, they had to go to a more complex design, with the vertical cam geared for two cycles to each cycle of the horizontal cam. The claws pull down a frame, then they go up, down without touching the film, and back up again before they engage and pull down again.

You can design a pulldown for pretty much any speed you want, limited mainly by the survival of the film on the fast end.





-- J.S.
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#5 Simon Wyss

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Posted 18 February 2011 - 01:58 PM

When they went to the cardioid cam, they were able to make it "dwell" at the top and bottom of the stroke, which allowed them to go to 180 degrees.

Nothing special Arri or anything new then. See this: http://de.wikipedia....Cinématographe, where you’ll find the came Carpentier of 1895.
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