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 Post subject: 180 Degree Shutter Rule
PostPosted: Fri Feb 12, 2010 10:26 pm 
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So, not everybody's camera will be able to be set up for this, but it is something that people with the 7D, 5DmkII, and any other camera with a more fully featured video mode should keep in mind.

http://blog.tylerginter.com/?p=385

Yes, its kind of a longer read, but I REALLY recommend it. There's a reason people want to keep making movies with film, and its because of the look of film. Digital is starting to emulate it more, but you won't even get close if you don't follow the 180 degree rule.


In general, if you're shooting video at 30fps, you want to be using 1/60th shutter speed. At 24fps, you want 1/48th. Basically doubling your FPS gives the correct shutter speed to shoot at to get 180 degree shutter. Full explanations on why, etc. found at the link!

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PostPosted: Fri Feb 12, 2010 11:25 pm 
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Thanks for the link. I've not seriously played with video yet, but will have to keep this in mind.

The sample video at the end does help illustrate the impact more than words describe.

I have to wonder how that scales though, for example if 1/60 at 60fps gives similar effect to 1/30 at 30fps. Intuitively I wonder if the absolute shutter might be dominant regardless of the framerate.

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PostPosted: Fri Feb 12, 2010 11:34 pm 
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I'd guess (though I'm not an expert and can't confirm as my camera doesn't allow for these settings) that 1/60th at 60fps and 1/30th at 30fps would be fairly similar. Since we see relatively smooth motion at 24fps I'm not sure we'd be able to tell the difference that between a 360 degree shutter angle at different fps/shutter speed settings (unless perhaps you're an expert). Assuming you stay above 24fps, shutter angle is going to have the greatest effect on the "smoothness" that you get.

[EDITED this paragraph out. I was wrong about what I said in it, so disregard if you read previously! See my next post for corrected version of what was said here.]

Actually, that got me curious so I went and looked. You do in fact use above 180 degree shutter angles to get motion blur without post processing. So, if that's what you're looking for, that's how you go about it.

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Last edited by Stig on Sat Feb 13, 2010 12:07 am, edited 1 time in total.

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PostPosted: Fri Feb 12, 2010 11:41 pm 
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I think I'll add this onto my list of "things I might test some day". Not familiar enough with how human vision works in that sense.

On that note, I wonder if that's why real time computer generated graphics (gaming etc) tend to feel the way they do even at stupidly high frame rates. Effective shutter time would be zero and no blur.

I was just thinking, how would you expose beyond 360 degrees? Your exposure time would exceed the time available for a single frame. You'd have to start merging frames together or equivalent.

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 Post subject:
PostPosted: Sat Feb 13, 2010 12:05 am 
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Well, after doing a bit more research it appears that, at least with real film cameras, you can't go above a 180 degree shutter. So anything above only applies to digital. At 180 degree each frame is only being exposed for 1/2 of the time that it is being shot. The other 1/2 of the time the shutter is closed. In film cameras that is so that you can advance the next frame into place while the shutter is closed. Opening up to 360 degree angle you're exposing the frame the whole time it is being shot, creating more motion blur.

You obviously couldn't do that with a film camera because the film physically moves past the shutter gate, meaning that you'd not only be creating motion blur but also have a very strange exposure on the film caused by the subject basically being moved across the frame from top to bottom...not good. The "advantage" to this in digital is that you can let more light into each frame, meaning you can use a lower ISO or a smaller aperture. The problem is the resulting motion blur is unnatural looking.

Anyway, moving on to your ACTUAL question from the last post (yes, I am getting there) at greater than 360 degree angle's you're basically doing multiple exposures. (I actually misinterpreted things in my previous post. I'm going to edit it to clarify/make it correct). So at 720 degree angle you're exposing each frame twice. At 540 each gets exposed 1.5 times, etc. While this allows in more light, it also causes much more motion blur.

At shutter angles BELOW 180, you're exposing each frame for less time. The example used in the blog is Saving Private Ryan, which achieved its staccato feel through use of 90 and 45 degree angles.

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