what is the normal shutter speed for feature movies?

[David Mullen ASC]

It's complicated to understand, even more me, but there are basically safe frame rates and shutter angle combinations. If you are shooting at 24 fps with a 144 degree shutter angle (1/60th of a second), you basically get two pulses per frame from a 60 Hz light -- same for a 25 fps camera with a 180 degree (1/50th) shutter shooting a 50 Hz light.

So a good starting point when setting the shutter on a video camera is to pick a shutter time that is 1/60th or 1/30th for a 60 Hz light (even 1/120th works I believe, but that's only one pulse captured per frame.) But that's only a starting point, you may need to play around a bit using the ECS.

The formula is any frame rate that divides evenly into twice the power frequency is safe. 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 24, 30, 40, 60, 120 fps for 60 Hz.

Anyway, here's a chart:
http://www.panavision.com.au/Informa...erfree60Hz.htm

Someone how understands math and electricity can explain it better than me...

But the principle is that flicker occurs when each frame exposed is getting a slightly different exposure than the proceeding or following frame, and this exposure variation appears as flicker. So there are certain combinations where the amount of AC pulsing captured is consistent frame to frame, and there are combinations where it isn't.

[Yousuf Abbasi]

I've been giving this some more thought, and am curious:

For a given a shutter angle and frame-rate, it is possible to calculate the exposure time (or shutter speed); BUT since this relationship does not take into account the area of the actual frame being exposed (e.g. 77-sqmm versus 346-sqmm), does that mean that a 16mm film frame and a 35mm film frame would be identically exposed under a given shutter angle in the same rotary disc? In other words, if the shutter angle is large enough to expose an ENTIRE 35mm frame, but you replace that frame with the smaller 16mm frame, will the exposures be identical (i.e. will the "extra" light just be ignored)?

More of a theoretical question, but I'm still curious. Hopefully I was clear, but in the likely event I was not, let me know and I will clarify.

[Stefan Christou]

If you were shooting film then no there would be no difference between exposures as long as you were using the same film stock, albeit cut into a different sized perforated ribon, to fit s16mm or s35mm.

This is the exact same thing as shooting cropping part of your sensor eg. 2k on Red One.

It doesn't matter if you are using different focal length lenses, as long as the T stop is the same in each case.

But if we are talking digital cameras, even using the same class of sensor, such as the forthcoming Scarlet s35mm and Scarlet 2/3", then the sensors would likely have different natural levels of sensitivity to light, and therefore will have a different level of exposure, just like if you used different ASA rated film stocks. (The sensors will probably have different levels of sensitivity because the smaller sensor will have more, smaller photo-sites packed on to the sensor, which have historically been less efficient at capturing light than their bigger brothers.)

I suppose the short answer is yes for film, as long as you are at the same T stop, but no if you are shooting digital.

[Yousuf Abbasi]

If you were shooting film then no there would be no difference between exposures as long as you were using the same film stock, albeit cut into a different sized perforated ribon, to fit s16mm or s35mm.

This is the exact same thing as shooting cropping part of your sensor eg. 2k on Red One.

It doesn't matter if you are using different focal length lenses, as long as the T stop is the same in each case.

But if we are talking digital cameras, even using the same class of sensor, such as the forthcoming Scarlet s35mm and Scarlet 2/3", then the sensors would likely have different natural levels of sensitivity to light, and therefore will have a different level of exposure, just like if you used different ASA rated film stocks. (The sensors will probably have different levels of sensitivity because the smaller sensor will have more, smaller photo-sites packed on to the sensor, which have historically been less efficient at capturing light than their bigger brothers.)

I suppose the short answer is yes for film, as long as you are at the same T stop, but no if you are shooting digital.

That's makes a lot of sense, and it's nice to get the digital-analogy too. Great job guys. It's so cool how much one can learn in this place!

[David Mullen ASC]

Other than the Arri D21, digital cameras have electronic shutters, so the size of the shutter blade relative to the sensor is a non-issue -- you set shutter speed by time (even when inputting a shutter angle).

There was only one movie camera that was switchable between 35mm and 16mm, the Eclair Cameflex, and switching didn't affect the exposure, the shutter exposed the film for the same length of time regardless of whether the gate was 16mm or 35mm in size.

[C. Kim Miles csc]

Another thing that David alluded to but maybe didn't say specifically is that a 1/48" exposure most accurately replicates the human eye's perception of the phenomenon known as "persistence of vision" and therefore provides the most natural-looking reproduction of normal movement.

If you look at (god forbid) a strip of film with motion in it, you'll see that the moving object in the frame is in fact blurred in each frame, yet when played back at normal speed, appears perfectly sharp. This is how the eye interprets movement, and is most accurately reproduced with a 1/48" exposure time.

Just my 2¢...