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High shutter speeds for Stroboscopic effect


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#1 Ashim

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Posted 31 October 2006 - 12:54 AM

Hi,

I was recently working on a Sony PD170 recently, and I decided that I needed a stroboscopic effect for some of the shots.

To get a stuttering look means faster shutter speeds, so I promptly increased my shutter speed from 1/50 to 1/200, the light intensity reduced but I didnt get the desired effect.
Then I set the shutter to 1/6 and was surprised to see the result I desired.

But how is this possible? Shouldnt the effect have taken place at higher shutter speeds akin to narrow shutter angles?

Kindly clear the doubt

Thanks
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#2 Ashim

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Posted 05 November 2006 - 01:03 AM

hello

Cld someone Kindly help me out here, please???
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#3 David Mullen ASC

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Posted 05 November 2006 - 02:22 AM

You're just talking about two different types of motion strobing -- one from having a very low frame/field (capture) rate and the other from having a short shutter speed but a normal rate.

If you set a interlaced-scan NTSC/PAL camera to something like 1/6th of a second shutter speed, then the frame rate HAS to drop below normal because it is not physically possible for a camera taking 60 fields per second to have a longer exposure time per field than 1/60th of a second, right?

So if you have an exposure time of 1/6th of a second, obviously the camera is doing it by slowing down the capture rate and then repeating fields to get the speed back to normal, thus you get the look of a low capture rate and long shutter speed -- which is just a different kind of strobing than a normal capture rate but a shorter-than-normal shutter speed.

It's like shooting a 6 fps on a film camera with a 180 degree shutter and then repeating frames to get back to 24 fps, versus shooting at 24 fps but with a 45 degree shutter angle. A good example of both effects occur in "Saving Private Ryan" and the opening battle in the forest in "Gladiator". Much of the battle in "Saving Private Ryan" was shot at 24 fps with a 45 degree shutter (thus a shutter speed of 1/192) but the POV shot where Tom Hanks sees the soldier pick up his own arm during the battle was shot at 6 or 8 fps and step-printed back to 24 fps. The same thing in "Gladiator" -- the first part of the forest battle was shot at 24 fps with a 45 degree shutter angle for most of the intense fighting, but when they lost the light, they switched to 6 or 8 fps with a 180 degree shutter angle to get more exposure and step-printed (repeated frames) to get back to 24 fps, or even more to create a slow-motion effect.

So you get the look of having too few frames with each frame containing a lot of blur.
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#4 Ashim

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Posted 05 November 2006 - 07:36 AM

David

Thanks a Lot. That was very informative.
Just one more thing.

By a Long Shutter Speed, you mean Shorter Shutter Speeds( 1/6,1/12), right?
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