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Old December 9th, 2014, 12:54 PM   #1
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Deviating from the 180-degree shutter rule?

In pursuit of the 'film look' sweet spot, I tend to shoot with the shutter speed at 1/50 (shooting 25P), and slavishly keep it locked off. Obviously this is not an ideal arrangement, as I lose one of my exposure tools, but it generally works out okay, with the judicious use of ND, ISO, etc.

But I gots to thinking:

1) If the whole idea is to replicate a certain ideal amount of motion blur associated with film, then wouldn't that amount remain the same (on today's cameras), at, presumably, 1/48 (24fps at 180). Why change to, say 1/60 if shooting 30P? Or does this have more to do with light flicker?

2) Since there seems to be some play in the exact amount of motion blur associated with film, what are the parameters, in shooters opinions, that you can work with and still approximate a traditional film feel?
I'm not talking about the creative deliberate breaking of the rule - like if you want to 'freeze' action ( la Saving Private Ryan, etc.), I mean - how far in each direction can I push shutter speed (I currently shoot DSLR), and stay within the realms of 'film look' association?

3) How come stills photographers would never consider hand-holding at 1/50 shutter speed, but we do it all the time? Surely we require sharp images too?

4) Is the 180-degree shutter rule a load of nonsense at high frame rates? Surely shooting at say, 1/240 (for 120fps) produces little to no motion blur, so how does that fit in with the 'film look' philosophy?

All the above in genuine curiosity.
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Old December 9th, 2014, 05:47 PM   #2
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Re: Deviating from the 180-degree shutter rule?

A 180 degree shutter will always expose the frame for half the amount of time that frame is "in the gate." In motion picture film cameras, the film is pulled into the gate (the area where it gets exposed) then the rotating shutter spins to the open position to expose the frame, then it continues to rotate until it is closed, then the film is advanced. The 180 degree shutter means that of the circular shutter (360 degrees) only half of it is open, the rest is black (or mirrored to reflect into a viewfinder.)

180 degrees became a standard for a good compromise between motion blur and light exposure. It's also easy to make a half-circle. The motion-blur aspect became part of that makes film look the way it does. Another aspect is frame rate.

In a 30 fps system, a 180 degree shutter would be one over double the frame rate, i.e. 1/60th second. In a 24 fps system, it's 1/48, and in a 25 fps system, it's 1/50th.

Now let me get to your questions by starting with your intro.

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Originally Posted by Aldon Davis View Post
Obviously this is not an ideal arrangement, as I lose one of my exposure tools...
Shutter should be locked at 180, unless you are doing something that requires a higher or lower frame rate. For instance, you want the blur of car tail lights passing you on the highway, or you're shooting action sports and want to choppy, clean motion with no blur. Always consider how you are affecting your motion when you change shutter angle/speed. Similarly to how you consider your depth of field when selecting a lens and f.stop.

1) I kind of answered that above. Yes, motion blur will change since you are exposing the frame for more or less time. 1/10th of a second difference (between 1/60th and 1/50th) won't be extremely noticeable though. The frame rate difference will be more noticeable than the motion blur.

2) 180 degrees at 24 fps (aka 1/48th second) is the standard. Period. A lot of film cameras don't have adjustable shutter angles even. You can change the angle, but that involves taking the camera apart and changing out the physical shutter.

3) Stills photogs are shooting one frame. Any motion blur they have in that frame will be shown for ever and ever in that photo print. Since we are shooting 24 photos each second, the brain blends them together and tricks itself into thinking it's actually moving. Motion blur actually helps sell the illusion, since motion blur occurs in real life.

4) At high frame rates, you've thrown motion blur out the window, since you are slowing down the motion. You can still shoot at a 180 degree shutter, but opening that up to a 90 degree shutter won't impose as much motion blur, since (relatively speaking) the objects aren't moving as fast.
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Old December 9th, 2014, 06:02 PM   #3
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Re: Deviating from the 180-degree shutter rule?

Thanks for the reply. I've got a pretty good handle on the mechanics of it all, and how it came to be a standard. I still question - what range of shutter speeds can you get away with in pursuit of a film look type standard? I get that 1/48 is ideal, but what else is acceptable visually (for film look)?

The answers given for 3) and 4) make absolute sense to me. Thanks again.
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Old December 9th, 2014, 06:04 PM   #4
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Re: Deviating from the 180-degree shutter rule?

I would do some tests. Take something that moves at a consistent rate, like a metronome or a house fan. Try some different shutter speeds and analyze the motion blur. Use 180 as a benchmark, and compare the rest to that.
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Old December 10th, 2014, 12:00 PM   #5
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Re: Deviating from the 180-degree shutter rule?

I'm definitely thinking of doing that. I'd love to know what other people's experiences are though.
There must be shooters who like that film look, but have ventured from 180-degree for one reason or another (caught without sufficient nd? Inadequate lighting?). What are people's experiences of the neighbourhood shutter speeds with regards to maintaining the integrity of the look?
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Old December 10th, 2014, 03:35 PM   #6
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Re: Deviating from the 180-degree shutter rule?

Aldon, 180 degrees is the theoretical maximum for a rotary shutter. Most film cameras shot around 170 to allow for frame slap, including Arriflex, even thought they claimed 180. Compound shutters on Mitchell's and Panaflex could shoot more than 180, mostly helpful in the days of 50 ASA film rather than to get a dreamy look. Some cameras (Bolex) had "bright light" settings around 120 degrees, some you had to use a different shutter (Arriflex). "Film look" from video is mostly a fools errand. Which film? You can get the look of a particular film by paying attention to production values, but the only way to get the illusory generic "film look" is to shoot on film or reverse telecine your footage - the film look isn't from the way footage is captured, it's from how it's shown. Shooting and showing video at 24fps especially doesn't get a film look, it gets a 24fps video look. 180 degrees is a reasonable rule of thumb, but that's all it is. Shoot some tests to see what fits the circumstance.
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Old December 11th, 2014, 12:48 PM   #7
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Re: Deviating from the 180-degree shutter rule?

Thanks. Sounds like great advice.
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Old December 16th, 2014, 09:24 AM   #8
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Re: Deviating from the 180-degree shutter rule?

If you are looking for a rule of thumb, I would say that 45 degrees one way or another from 180 would be the most you could go without the effect starting to becoming noticeable, i.e. a 135 degree shutter would be on the edge of perceptible but a 90 degree shutter definitely has it's own look aka "skinny shutter". It doesn't make it less film-like, because as noted above we sometimes used to skinny the shutter when shooting film for the effect anyway, although anything greater than 180 degrees (especially shutter off) was physically impossible in the film days and thus not a great idea. "Apocalypto" was one of the first large chip feature films (on the Panavision Genesis) and they sometimes turned off the shutter to get more stop in the forest, resulting in a blurrier image that in many people's mind marred the visuals.

There are times when I will use a skinnier shutter specifically because it eliminates some motion blur, not so much as an effect. One would be shooting close-ups of someone running or dancing, since their constant motion will make it look almost out of focus, continual motion blur, so I will elect to drop the shutter to 135 or 90 degrees to avoid this. That cuts fine with wider shots at 180 degrees. I'm fairly sure I used this technique in this sketch but sadly--didn't take notes so I can't remember!

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