Shutter Speeds

[Cris Moris]

Hey,

 

So I was shooting some tests with my XL1 earlier for no reason just cus. I bumped the shutter speed to 2000. I was shooting objects in motion ie: a fan, running water, water drops. I wanted to see how it looked when I increased the shutter speed. The result I'm sure you are all familiar with is: that sort of frozen look of the objetcs in motion (hard to describe). Nuturally this occurs because of the fast shutter speed.

 

My question is can this look be achieved with a motion picture camera without changing the Frame rate? Is it a matter of changing the shutter angle? And what is the fastest shutter speed one can achieve? I understand that all this may require a lot of light, so this is all hypothetically.

 

I think something similar was done in NARC, maybe in the begining sequense?

 

Just curious. Thanks

[David Mullen ASC]

It's actually easier to shorten the shutter speed without changing the frame rate than it is to make it longer than the normal 180 degree shutter allows (1/48th of a second at 24 fps.)

 

By closing the shutter angle down from a half-circle (180 degrees, so the image is exposed for half the time of the frame rate) to a quarter circle (90 degrees), you cut exposure time in half, from 1/48th to 1/96th. Close it down by half again, to 45 degrees, and the exposure time is 1/192nd at 24 fps. I haven't heard of anyone closing down the shutter even more than that -- I'd think there wouldn't be enough room for the film gate to be completely open anymore.

 

Usually shorter exposure times than that are accomplished by then either raising the frame rate or by using strobe lighting.

[Adam Frisch FSF]

Yes. Most camera types can change the shutter angle - all the Panavisions and Arris and Aatons of later models do it at the flick of a button. Normally from 180 down to about 11,5 degrees.

 

It's an almost overused look these days (I can't stand it at the moment, frankly)

made famous basically by the opening shots of Saving Private Ryan, although I believe

it had been used for quite some time in music videos and commercials before.

 

It adds an edge and can sometimes enhance a storypoint, but mostly is just done out of laziness these days. It does however serve quite a useful function in high speed photography - especially liquids and such look great in slo-mo and short shutters to "freeze" every droplet.

 

Also, down to about 90 degrees on not very fast moving objects, it's almost invisible which gives

you a 1 stop latitude to play around with if you need to control light but don't want to hang more

ND or whatever in front of the lens.

[Cris Moris]

By closing the shutter angle down from a half-circle (180 degrees, so the image is exposed for half the time of the frame rate) to a quarter circle (90 degrees), you cut exposure time in half, from 1/48th to 1/96th. Close it down by half again, to 45 degrees, and the exposure time is 1/192nd at 24 fps.

 

Usually shorter exposure times than that are accomplished by then either raising the frame rate or by using strobe lighting.

Hey David,

 

Thanks for the reply. So a change in degree means a change in stop also right?

 

Let say I start with a F2.8 at 180 shutter 24fps. At 90 degrees the new stop would be F2.0?

 

Also, I'm not quite sure I follow the strobe thing. I kind of have an idea but need further explaining...

 

Thanks

[Michael Nash]

Thanks for the reply.  So a change in degree means a change in stop also right?

 

Let say I start with a F2.8 at 180 shutter 24fps.  At 90 degrees the new stop  would  be F2.0?

 

can refresh very quickly and also sych to the camera.

You got it. Cutting the shutter angle in half means an exposure of half as much light, or one stop. Cutting the 90 degree shutter down to 45 would be one more stop, or f 1.4. You may have noticed as much with your XL-1 -- your exposure got darker with the fast shutter until you opened the iris (or the auto iris compensated).

 

Strobe lighting works pretty much the same way it does with stills, except that the strobe has to be synched to the camera's shutter. The quick pulse of light exposes one frame of film, and when the flash turns off there is effectively no exposure left, regardless of the shutter angle. The camera then advances one frame and the flash goes off again, 24fps (or whatever you like).

 

Needless to say you need a strobe system (like Unilux) that can refresh very quickly and can synch to the camera. Strobes are often used this way in high-speed closeup photography (like those food commercials where you see a head of lettuce crashing through cascade of water), and also in settings where the light and heat of regular lights would be too much for the subject (again, think of wilting lettuce).

[David Mullen ASC]

Think of it this way. In a pitch-black room, it doesn't matter what the camera's shutter speed is -- the duration of the strobe flash becomes the effective exposure time per frame. So while your camera shutter may be open for 1/48th of a second, the illumination is only "on" for 1/1000th of a second, let's say, so that becomes the true exposure time.

[John Pytlak RIP]

Using a strobe on an action scene that is also lit with continuous light (daylight or HMI) with a normal shutter angle will give a mix of motion blur and sharp image, depending on the sync of the strobe. Has anyone done this?

[Adam Frisch FSF]

They did a Mazda (or was it Ford?) commercial years ago where the car drove on a country road. The blasted it with Unilux lights so that the background and scenery got all motion blurred, b ut the car stayed sharp. Didn't see it, just read about it in AC.