need help about shutter angle

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#1 john jayapaul

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Posted 14 March 2007 - 08:39 AM

hello

I am john, now working as a assistant cinematographer in india, chennai, I have a doubt in shutter angle, please help me.

my first question, how do I get a sharp image with shutter angle, I use arri 435 es model camera and elite lens, what is the effective shutter angle for arri 435 es.

please give me some notes about all the cameras and their shutter angles so that, I may be able to hire them from the company,

and please tell me the frame rates of different format eg: motion film camera, dvs, etc;

please help me, I am in desperate need of it,

thank in advance

john
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#2 David Mullen ASC

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Posted 14 March 2007 - 11:56 AM

Standard shutter angle is usually 180 degrees, which is a half-circle (the shutter is a spinning disc with a pie-slice opening to allow light through). At 24 fps, therefore, the shutter is open for half that time, so the shutter speed is 1/48th of a second (half of 1/24th of a second.)

You don't improve overall sharpness at different shutter angles, but you can sharpen the motion by reducing the amount of blur by going to shutter speeds shorter than normal (like at 90 or 45 degrees.) Since 90 is half of 180, you lose a stop of exposure since the shutter speed at 24 fps goes from 1/48 to 1/96 of a second. 45 degrees is half that again, so 1/192.

Unfortunately, since 24 fps is a rather low frame rate to capture motion at, you need motion blur to create some smoothness, so if you sharpen the motion too much by using short shutter speeds, you get strobing (see the action scenes in "Gladiator" or "Saving Private Ryan" to see the effect of strobing from use of closed-down shutter angles like 45 degrees.)

There also other shutter speeds for use when filming an NTSC TV set at 24 fps (144 degrees) or when shooting under 50 hz lighting, or when shooting at 25 fps under 60 Hz lighting, etc.

Typical video interlaced-scan camera is either 50i (PAL) or 60i (NTSC), and usually is shot with the electronic shutter turned off, so the exposure is the same length as the field rate (1/50th for 50i / 1/60th for 60i.) You can use shorter exposure times if you want for effect, like 1/100th, etc. A 24P progressive-scan video camera will allow shutter speeds of 1/24, maybe 1/32, 1/48, 1/50, 1/60, 1/100, etc.

A few interlaced-scan cameras offer shutter speeds that are slower than the field rate, which seems physically impossible (i.e. if your camera is taking a picture as a field 60 times per second, how can you have an exposure time longer than 1/60th of a second?) They do this by actually slowing down the capture rate, using a frame buffer, and rewriting fields in order to get the speed back to normal. So you may see a video camera with a shutter speed setting of 1/2 of a second, let's say, which would create very strobey yet blurry motion.
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#3 Chris Keth

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Posted 14 March 2007 - 12:25 PM

Perhaps it helps to think of shutter angle changes as changes in shutter speed without any change in frequency of the images.
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#4 Michael Nash

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Posted 14 March 2007 - 02:25 PM

please give me some notes about all the cameras and their shutter angles so that, I may be able to hire them from the company,

The "ES" in the Arri 435 ES name stands for "electronic shutter." That means that the shutter angle is adjustable electronically, not just mechanically. You can program the camera to change shutter angle while the camera is running, as a way of maintaining correct exposure during speed ramps (among other things).

The best way to become familiar with the range of frame rates and shutter angles available with different cameras is to get a guidebook such as:

Professional Cameraman's Handbook
Hands-On Manual for Cinematographers
American Cinematographer Manual

After that you can get familiar with the cameras available in your area, since cameras are often modified beyond their original specs.
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#5 john jayapaul

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Posted 17 March 2007 - 09:21 AM

thank you for your replies,,

now I understood how to work with shutter angle, please tell me is there any ebooks available so that I could learn,

I will be buying some of the books you have mentioned, but please help me to get some ebooks.

thanking you

john
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#6 john jayapaul

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Posted 18 March 2007 - 09:00 AM

thank you for your replies,,

now I understood how to work with shutter angle, please tell me is there any ebooks available so that I could learn,

I will be buying some of the books you have mentioned, but please help me to get some ebooks.

thanking you

john
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#7 Jon Kukla

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Posted 18 March 2007 - 04:02 PM

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