Shutter Angle

T

THiNSPiRiT

Well-known member
Just learned something cool from film school... the difference between shutter speed and shutter angle and why on film cameras it's a shutter angle not a shutter speed...

A shutter angle is based on the fact that a film camera has a disc that spins around in the camera after the lens before it hits the film. This disc has a slight piece of the pie cut out depending on how much light you'd like to have let in to expose the film. The larger the piece of pie, the greater the shutter angle and the more light that is let in.

a 90' shutter angle would mean a quarter of the disc is taken out. The disc still spins at the same speed as it would with a 180' shutter angle, but the 180' would let in more light.

I'm sure a great deal of you already know this, but for those of you who don't, it's pretty cool...

This also means though that when shooting on film, different parts of the frame are exposed at slightly different moments in time. So minor that the human eye wouldn't really notice, but subconsciously we might...

Another reason why the viper cam is so awesome. It uses this mechanical film shutter to expose the CCD to light rather than using the electrical shutter speed that most digital cameras use...
 
Re: Shutter Angle

I think of shutter angle as a way of manipulating the amount of motion blur we see on film.

I for a long time thought the motion characteristics achieved in the opening D-Day scene in "Saving Private Ryan" as well as the opening battle scene in "Gladiator" was achieved through film speed or shutter speed. I was told by a DP that this was not really true. Much of this jittery motion effect is achieved through the shutter angle.

This was further confirmed to me while working in the digital realm in 3D Studio Max. Max allows you to adjust the shutter angle, which affects the amount of motion blur you get in your animations. In Max, the higher the numerical value on the shutter angle, the more the motion blur.

The Varicam allows you to adjust shutter angle like a film camera, and I've seen this jittery effect achieved in that camera.

I can't say I'm 100% positive on this, if I'm wrong please someone correct me!
 
Re: Shutter Angle

You're right, but that's over-simplifying it a bit. The shutter angle is really quite equivalent to the "shutter speed" in terms of its effect. A 180 degree shutter at 24fps is open half the time, so this is equivalent to a 1/48th of a second shutter speed on the dvx. It's no surprise then that the dvx's default for 24p is 1/48th-1/50th of a second, given that 180º shutters are so common with 35mm film. "Shutter speed" is really just a cheaper way to emulate the true "shutter angle" so it makes sense that a lot of effects videographers try to achieve with shutter speed were achieved initially with the shutter angle on film.

I'm not convinced it's a perfect emulation, however, as film (at least during pans and tilts) seems blurrier and softer than video. A mechanical process often has more complex stuff going on than its electronically simulated counterpart. Anyhow, I'm still dying to see a 35mm versus dvx100 pan test where the nature of the motion blur each creates is studied in depth. Either that or I'll just start shooting moving shots at 1/36th of a second shutter speed, which is the lamest way out one can imagine but a simple solution to strobing.

Also, it is kind of cool that parts of the frame are exposed at different times, though the shutter is so fast that this probably doesn't make a difference.
 
Re: Shutter Angle

.. in video terms.. aside from a camera like the viper filmstream
there is no such thing as a shutter angle on a video camera since is has no mechanical shutter. instead the shutter is electronic, and only the shutter speed dictates the equivilant shutter angle. for example a shutter angle on a film camera of 180 at 24fps would be the same as a shutter speed on a video camera of 1/48 @ 24fps.. its the same  thing for all practical purposes. the shutter will expose the imaging recording medium for 1/2 of the frame time.

  the shutter angle on a film camera determines the amount of exposure time for the film frame, and the shutter speed on a video camera determines the amount exposure time on the electronic sensor. and the motion rendering resulting is virtually the same.(again only differing in the fact that the mechanical shutter exposes the frame with an imperceptable temporal difference throughout the frame).. barry green has done motion rendering tests to prove the motion rendering is indifferent..


..sure the spinning mechanical shutter will expose the film frame at slightly differnt times  vs the electronic shutter on a video camera exposing the frame all at once, but the differences in motion rendering are really imperceptable to the human eye. its not really an issue of a different amount of blur imposed, but is an issue of the temporal differences betweeen the exposure of the top of a film frame through to the bottom.  but the motion blur induced throughout the frame is the same as if it were exposed at one instance  since any given portion of the frame was only exposed for the same amount of time.

anyhow even the DVX can achieve saving private ryan motion jitter effects for that "staccato" look on playback.. just by using a higher shutter speed such as anything 1/120th or higher  you will  begin to notice more and more of a staccato effect, by the frames containing less and less motion blur.

natob2- your correct in your thinking,  but the same things can be achived through shutter speed in the video world :)

in the film world shutter speed can be variable too on some cams as well, which will do the same thing.. control exposure time.

edit-sorry policar.. wa typing when you were.. doubled up some of your info..
 
Re: Shutter Angle

It's sort of a misconception that film cameras usually operate at 180°, which is why it's so odd that 24p alone has been taken as the holy grail of film emulation.

There are a wide variety of film cameras out there, including some turn of the century models that are still quite in use today. Many fixed shutter cameras didn't come standard with 180° movement. By designing their cameras with a more accute shutter in some cases, they could give more time to the mechanics for frame advancing since the shutter was open for a shorter period of time.

Now are the days of variable mechanical shutters and electronic variable shutters that can often be adjusted anywhere from 11.2°-180°. Cinematographers have more control over exposure and motion blur through adjustments of the shutter angle...and with an electronic variable shutter angle they can do speed ramping without changing the iris.

In my experience, cinematographers use 133°, 144°, 160°, 170° and 172.8° as a baseline more often then 180°. Each has a different look on film because it captures motion differently and limits light accordingly.

Also, for the sake of accuracy, the saving private ryan footage also used a slightly mistimed shutter to emulate the shutter flaring seen in historical WWII combat footage.
 
Re: Shutter Angle

[quote author=Policar link=board=Offtopic;num=1095227494;start=0#2 date=09/15/04 at 07:38:14]Anyhow, I'm still dying to see a 35mm versus dvx100 pan test where the nature of the motion blur each creates is studied in depth.[/quote]
My upcoming DVX book/DVD has a section devoted to this, and the DVD has extensive panning shots side-by-side with the DVX and 16mm film, which is pretty much exactly what you're asking for.

Why didn't I use 35mm? Because some people are insisting that the DVX looks "strobier" than film because of the shallower DOF typical of 35mm shots. The reasoning goes that since the DVX's background is usually sharply in focus, vs. film's background being out of focus, that one notices the strobing more. My plan was to shoot in bright outdoors light, on maximum wide angle (10mm on the 16mm camera), getting an identical field of view, with an f-stop of around f/11. That way everything from the front of the lens to infinity would be sharply in focus on both cameras. It should remove the "focus" angle from the argument, and allow us to see whether DVX motion renders the same as 16mm motion or not.
 
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Barry Green, you continue to amaze me. That's a very well thought out test and I'm looking forward to seeing the results. Can you spoil the surprise and tell us what your testing revealed?

The DOF theory was actually my own (sharp objects being tracked in foreground, background too blurry to be strobey) but I think a lot of people thought of that idea before I did.
 
Re: Shutter Angle

I've heard the concept pitched before, but I don't remember who said it first -- it may be a Policar original!

As for test results, I'm still working on that segment so I don't want to comment yet. There's so darn much to do on this thing... ;)
 
Re: Shutter Angle

This conversation is leading dangerously close to the dreaded "circle of confusion" argument.
 
Re: Shutter Angle

A simple but true detail about the shutter spinning disk in a film camera is that what you see through the eyepiece is through the 'open piece of pie' whilst the rest of the disk is masking the aperture to the film.

So in practice if you see something in the eyepice, the film is not seeing it and vice versa. For regular moving objects, thats fine but if you were to . . . lets say . . . strobe a light at the same speed as the camera (24fps) and you are seeing the light in the eyepiece, then the camera will not see it, or a more practicle example would be seeing a fast gun shot flame in the eyepiece may not be on your film.

The disk slowing down is usualy that flicker you see on Video Villages monitors.
 
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Ok, this is probably gonna sound stupid but since you can take the lens off the XL2, is it possible to make 35mm adapter for the XL2 with a physical shutter.
 
Re: Shutter Angle

Er... well, I guess so... or maybe not. Depends on how slow the slow-shutter speed of the XL2 goes. You'll still have the electronic shutter, but if you set the electronic shutter to expose for longer than the mechanical shutter, it shouldn't make a difference HOW long it exposes for, as long as all it's seeing is the black of the closed mechanical shutter. If you could sync the two... then yeah, sounds like it could theoretically be possible...
 
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