Slow Shutter

David Frank · March 29, 2005

Hi, I have been racking my brain trying to figure out how slow shutter speeds are achieved with motion picture film cameras. It seems like many adjustable shutters allow for fast shutters, but not slow. How is this done?

Dominic Case · March 29, 2005

It's not!

Some cameras can open their shutters to a little more than 180 deg - but I think 210 or 220 is about the limit - giving about 1/3 stop extra. Some digital cameras can have a "360deg" setting, which is effectively a 1/24th sec exposure at 24 fps.

Slower than that you can't do except by slowing down the frame rate.

David Frank · March 29, 2005

Hmm...thanks for that clarification. Just to make sure I totally understand. To get a motion blurred and brighter image similar to slow shutter speeds in the video world, I would have to shoot a lower frame rate? And if that's the case, how do I slow the footage back down to normal speed? Is this done in the telecine process if you were going to video?

John Pytlak RIP · March 30, 2005

The shutter must cover the film while it is being pulled into position within the camera, otherwise the lighter parts of the scene will cause streaks if the film is still moving while the shutter is open. In projection, an insufficient or mistimed shutter is called "travel ghost".

If you really want more motion blur than the typical 1/48 second of a 180 degree shutter at 24fps, you will need to film at a slower frame rate, and "stretch" the action during transfer or optical printing. For example, at 12fps, the exposure time is 1/24 second, but you can use each frame twice to keep the action at 24fps.

Alvin Pingol · March 30, 2005

>>To get a motion blurred and brighter image similar to slow shutter speeds in

>>the video world, I would have to shoot a lower frame rate?

Yes, as this allows each frame to capture a longer period of time, meaning more blur and increased exposure.

>>And if that's the case, how do I slow the footage back down to normal speed?

You mean speed it up? Normally, footage shot with slower framerates is not sped up, but rather printed with duplicate frames to get back to 24fps. If you were to speed up the footage, everything would be playing in fast-forward.

In fact, a lot of fight sequences in martial arts films are shot at ~22fps and sped up to 24fps. This is done to increase the speed of the choreography, as well as to keep things safer on set. Full-speed, full-power martial arts is deadly!