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#1 J. Scott Portingale

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Posted 13 May 2009 - 04:39 PM

I am fairly new to experimental cinematography, and I was wondering if there were any links to videos of slow motion in tandem with acute shutter angles that would also give technical details stating what angle they used, and what frame rate they shot. I am trying to figure out what angle I should shoot before rolling film through a camera at fast speeds. I will most likely shoot as fast as the camera will let me, but the angle still confuses me.

Actually here's a better question... What is 10degrees equivalent to in seconds? 1/250? 1/500?


ie: knife through head of lettuce (96fps) beads of water with clear tack sharp edges.
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#2 Kevin Zanit

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Posted 13 May 2009 - 05:06 PM

Stuff at the beginning of my reel - www.kevinzanit.com was shot at 1000fps with a 180 degree shutter.
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#3 J. Scott Portingale

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Posted 13 May 2009 - 05:06 PM

OK I just found this data, but it relates to 24fps.
what about 96fps or 150fps?
Is there a downlodable table out there I can refer to?

SLS 4 = 1440 degrees (try doing that with a film camera!)
SLS 2 = 720 degrees
1/24 = 360 degrees
1/48 = 180 degrees
1/96 = 90 degrees
1/192 = 45 degrees
1/384 = 22.5 degrees
1/768 = 11.25 degrees
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#4 J. Scott Portingale

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Posted 13 May 2009 - 05:16 PM

Thanks Kevin.

Your reel was impressive. I loved the slow motion! I always imagined that you would have to change the shutter angle to achieve sharp edges for filmming anything in motion.
What kind of lighting do you use for slow motion?
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#5 Kevin Zanit

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Posted 13 May 2009 - 05:31 PM

Thanks!

Well the high frame rate does give you a fairly short exposure time just by being at 1000fps. 1000fps with a 180 degree shutter is a 1/2000th of a second exposure. This is enough to freeze most actions. Things like small water drops and to some extent pours can benefit from an even tighter shutter, like 90 or 45 degrees, but that just requires a TON more light.

Most of those shots were lit with 5k, 10k and 20k fresnels.
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#6 Scott Fritzshall

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Posted 13 May 2009 - 05:41 PM

It's actually really simple math to figure this out. Film cameras generally use a 180deg shutter. What this means is that for every frame, the shutter is closed while the film is being advanced and open while the film is being held in the gate. 180deg is half of a full circle, or 50%, so each frame is exposed for half of the frame rate. At 24fps, each frame thus gets 1/48th of a second worth of exposure (1/24 x .5), which obviously affects both exposure and amount of motion blur. This is what you're generally used to seeing. If you speed the frame rate up 2x to 48fps, each frame is still exposed for 50% of the frame rate. Your exposure time is 1/96th of a second (1/48 x .5). This gives you half of the exposure time per frame, which means you lose a stop of light, and you get half as much motion blur. Still, as far as motion blur is concerned, you're still exposing for the same percentage of the frame rate, which is going to give it the same perception of blur. In other words, you've got half as much motion blur, but you've also got half as much motion, so it looks "normal, but slow."

Changing the shutter angle changes the exposure and the amount of motion blur, but it does not change the speed at which the action is being recorded. At 24fps, if you set the shutter to 90deg, you've got half as much exposure, and half as much motion blur. 90degrees is 25% of 360degrees, so your exposure is 1/96th of a second (1/24 x .25). Again, the rate at which things move does not change, but the amount of blur and exposure does.

So if you combine the two, you're going to get slower motion, less motion blur, and much less exposure time. Shooting 120fps with a 45deg shutter, for instance, will give you 1/960th of a second exposure time (1/120 x .125). Everything will move at 1/5th its normal rate, and also have 1/4th its normal amount of motion blur. In order to work out what values you need, you've got to figure out how long the event takes place in real life, and how long you need it to last on screen. If it lasts half a second and you need it on screen for 2 seconds, then you need to shoot it 4x the normal rate. At very high speeds, the exposure time is so low that you're naturally going to have very little motion blur, but if you want the action to have less than its "natural" amount, you can reduce the shutter speed to make each frame more "crisp," and the overall motion choppy.

Obviously, though, you're going to need a pretty massive amount of light in order to shoot that. In my example of 120fps and a 45deg shutter, the exposure time of 1/960th of a second means you need 40x more light, which is over 5 stops. Better pull out the Softsuns or whatever.

Does that help?
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#7 J. Scott Portingale

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Posted 13 May 2009 - 05:46 PM

Thanks for that. It was very informative. I will print that off, and add it to my production notes.

Thanks again!
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