Understanding “Film-Style” Shutter & SLR video

One of the most common issues that newcomers to SLR video struggle with is shutter speed. What shutter speed is most “cinematic,” and why?

To understand shutter speed for SLR video, it helps to understand how the shutter works on a traditional motion-picture film camera.


Film camera shutter open

film camera shutter closed

Inside a film camera, there is a rotary shutter, which is shaped like a semicircle. When the camera operates, the shutter mechanism turns continually; when it is “open” (letting light hit the film), an image is being exposed. When it “closed” (blocking light from the film), the next frame is being moved into place.

Regardless of what speed the film itself is running through the camera, half the time the shutter is open, exposing the film, and half the time, the shutter is closed, advancing the film.

This is important, because it means that with a film camera, your shutter speed – how long each image is exposed to light – is half your framerate – how many images are exposed each second. So, if you were shooting at the cinematic standard framerate of 24 frames per second, your shutterspeed would be half that – 1/48 of a second.

 

Rotary Shutter at 45 degreesNow, I’ve cheated a little bit by referring to the shutter as a semicircle. In reality, many motion-picture film camera shutters are adjustable. Imagine two semicircles pinned together: the amount of space left open could never be MORE than 180 degrees (half a circle), but it could be LESS, if you fanned the two semicircles out so that they left a smaller space exposed. That angle of exposed space is called the shutter angle. The standard shutter angle is 180 degrees – half a circle. But, for aesthetic or logistical reasons, sometimes angles of less than 180 are used, which means that the amount of time each frame is exposed to light is actually less than half the framerate.

What this means is that, if you set the shutter speed on your DSLR to more than half of YOUR framerate, you are simulating a smaller shutter angle. It’s not necessarily bad, but you need to be aware that is an aesthetic decision.

So, bottom line: the traditional standard for narrative filmmaking is a framerate of 24 frames per second, with a 180 degree shutter, which means a shutter speed of 1/48. So, if you want to do narrative filmmaking with your DSLR, you want to stay as close to that as you can.

But, keep that “half your framerate” shutter speed formula in mind. If you’re shooting at significantly higher framerates, and you want to stay faithful to the cinematic standard, you’ll need to adjust your shutterspeed accordingly.

One caveat: If you’re shooting under artificial light, and you start noticing strange banding or strobing in your image, it’s probably because your lamps are cycling at 60 khz, while your shutter is at 1/50. To compensate for this, set your shutter speed to 1/60.

With all that said, remember that rules are made to be broken. Absolutely terrific videos have been shot with no regard to “correct” shutter speed. Here’s a great example of footage shot with a shutter speed around 1/1000:

  3 comments for “Understanding “Film-Style” Shutter & SLR video

  1. Chris
    November 7, 2010 at 7:40 am

    Actually, the shutter never pauses as you mention above, it is in constant rotation. It’s during the time that the mirrored part of the shutter deflects film to the eyepiece that the film is in transport. The regi pin goes in, the shutter clears to expose the film, and on and on.

    • November 7, 2010 at 5:13 pm

      Great catch, Chris. I was trying to convey that the film itself pauses when it is being exposed, to explain why it then needed to be advanced to the next frame. However, you rightly pointed out that it sounded as though I was saying that the shutter itself pauses. I’ve edited the post to reflect your correction.

  2. Lianna
    January 11, 2013 at 6:39 pm

    Hey, I’m building a camera for my 4th year thesis and would love some expertise on building a rotary disc shutter. All info is posted here: http://www.apug.org/forums/forum147/114294-need-help-designing-3-shot-camera.html#post1445350

    If you have any advice, I’d love to hear it!

Leave a Reply

Your email address will not be published. Required fields are marked *