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A question about motion cadence


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#1 Hendrikus De Vaan

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Posted 03 November 2014 - 05:58 AM

Hi, firstly let me say that I'm a director, not a cinematographer.

 

I'm in pre-production for my first feature now, with the second in development. 

 

Lately, with the change to digital shooting and projection, I've been noticing a lot of difference in the way motion appears on the screen, both within camera movement and general movement of things in the frame. I can't quite describe it, but things no longer seem to flow like they used to. To my eye, there is a lot of visual stutter. I'm not sure if "motion cadence" is the right description for this?

 

Does this have to do primarily with shutter types? As in, rolling, global and soft global. From my guess, film was a sort of soft global with the spinning shutter, and this led to images seamlessly blending (or blurring) together.

 

Or, is this a byproduct of digital projection, where with the lack of a frame transition, with hard frame to frame refresh, it doesn't leave room for the brain to interpolate the frames?

 

Either way, I'd love to hear some thoughts on this, as I really don't know a whole lot about it, but motion cadence is an important thing to me, as I find even the slightest stutter very jarring to my own eyes (although when I've mentioned it to other people, they don't seem to know what I'm talking about).

 

Thanks in advance!

Harrie


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#2 David Mullen ASC

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Posted 03 November 2014 - 10:58 AM

I'm sure electronic shutters are a bit "crisper", more on/off, but if the shutter time is the same, it's a pretty subtle thing.  Probably more visible with cheaper cameras that have less dynamic range, the harsher contrast and sharpened edges to objects probably make the blurred edges less soft.

 

Movies also have been using short shutter angles for action scenes for a while now, so that's another element.

 

I don't think it's anywhere near as bad as not giving the brain time to absorb the image or anything like that.


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#3 Hendrikus De Vaan

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Posted 03 November 2014 - 11:39 AM

I might just be crazy, but I almost feel like there is more to it than dynamic range and crisper shutters. I watched a medium budget drama feature film shot on an Alexa, and the stutter in the pans was really quite bad to my eyes. That being said, it may be like you said an issue of shutter angle.

 

A friends was mentioning to me that it might be a case of them, and I paraphrase, "not using the pan and tilt rules outlined in the ASC handbook". I'm assuming this has something to do with the combination of shutter angle, lens length, and speed of panning?

 

The thing is, I often notice it in slower movements too.

 

I never really noticed it with 35mm or 16mm, so I sort of just jumped to the conclusion that it was just something that came with digital, but then it's barely existent in some digitally shot films.

 

Mainly I just want to get to the bottom of this as to avoid it in my own films, even if it's something most people might not notice.


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#4 David Mullen ASC

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Posted 03 November 2014 - 12:06 PM

Stutter is always a problem with anything captured at 24 fps, film or digital.  It's barely fast enough to record faster motion smoothly, hence all the old rules about safe panning speeds.  It's just the nature of sampling motion at such a minimal rate.  

 

But people complain about 48 fps and 60 fps capture and presentation as looking too "real", too "live", too "video" -- they are used to the stutter, staccato, etc. of 24 fps.  Traditional interlaced-scan video cameras sampled motion at a much higher rate, 50 times or 60 times a second, and often with no shutter, so people associate that very smooth blurred motion with video now.


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#5 David Mullen ASC

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Posted 03 November 2014 - 12:11 PM

I recently saw some experiments where someone shot at something like 120 fps and converted it to 24 fps using some sort of interpolation algorithm to smooth motion and imitate the effect of a rotating shutter in terms of feathering off exposure, it solved problems like the picket fence effect, wheels going backwards, etc. The motion was more pleasant but I can't really say it was worth the trouble of shooting at 120 fps., I wasn't bothered by the old artifacts.


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#6 Phil Holland

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Posted 04 November 2014 - 08:40 AM

Got your message Harrie.

 

What David is mentioning about the "safe" panning speeds applies here for 24fps.  To some this also influences the camera movement when focusing or following a subject as well with smaller movements in frame.

 

One of the more interesting things I've been tinkering with lately is utilizing the Red Motion Mount's "Soft Shutter" mode.  This particular effect reduces temporal aliasing, however, it does change the general character of the motion blur itself.  You do indeed get a smoother feel and a more painterly style of blur which increasing the focus on the subject matter slightly due to the different style of blur.

 

A good example I saw recently of that on the big screen was in Gone Girl when Detective Bony first pulls up to the house in her police car.  It's a crane move with the pan and tilt focusing on the car pulling into the driveway.  It's a fairly large pan, but the Soft Shutter effect shows off what's possible there.

 

In shots that do exhibit undesirable judder there's always post motion flow and blurring effects.  Most of the time I try to shoot within the boundaries that can be found in the ASC Manual though.  It's worked well for a few decades! 

 

One thing you can do is shoot with a fatter/wider shutter, like 360 degrees.  That's 1/24th for a 24fps time base.  That will give you more blur and lessen judder for certain moves.  I've certainly used this method on bigger moves.


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#7 Hendrikus De Vaan

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Posted 04 November 2014 - 09:33 AM

Thanks guys, really appreciate your thoughts and input.

 

I'll do some more reading into the motion mount, this is actually what I was referring to when I mentioned the soft global shutter. It sounds like this almost emulates a physical rotary shutter, which I think only one or two digital cinema cameras have.

 

So basically, the options are Red with a motion mount, F65, or shooting on film right? (of course adhering to the panning rules helps a lot of this too).

 

Thanks again!

 

Harrie


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#8 David Mullen ASC

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Posted 04 November 2014 - 11:00 AM

Alexa Studio has a mechanical shutter too.


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#9 Hendrikus De Vaan

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Posted 04 November 2014 - 11:34 AM

Thanks David, good to know.

 

And of course some older options, like the f23 for something closer to 16mm c.o.c aesthetic I guess.

 

I somehow like the motion cadence coming out of the f35 that I've seen too, but this might be purely circumstantial to the footage I saw.


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#10 John E Clark

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Posted 04 November 2014 - 11:58 AM


One thing you can do is shoot with a fatter/wider shutter, like 360 degrees.  That's 1/24th for a 24fps time base.  That will give you more blur and lessen judder for certain moves.  I've certainly used this method on bigger moves.

 

I was taking some grab shots with my Blackmagic pocket camera, just to see what ISO 1600 would do in a 'night street scene' with nothing but street lighting...

 

Anyway, as I was shooting, I tested 360 deg shutter, to get another stop's worth of light, it occurred to me that the taillight 'tracks' would be longer... but then it also occurred to me that in a 'real™' Hollywood shoot perhaps the traffic would be slowed (given the production has total control over the street traffic...), to conform to various transit speed limits to limit 'judder' and the like.

 

I do know that there's the recommendation for driving at slower speeds when shooting from the car interior 'outward'. But is there the same consideration for exterior shots where cars are driving past a camera on the side of the road?


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#11 David Mullen ASC

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Posted 04 November 2014 - 01:25 PM

Shooting with a 360 degree shutter is rarely done in regular movies, just as shooting a scene at 12 fps to get more exposure is rarely done, but occasionally it happens.  And when it happens, you might adjust some of the speed of things to hide the cheat.

 

A wide shot of traffic going by is likely to not be movie drivers following instructions on how fast to drive by, it's going to be the general public so the only way to slow them down is to put your own drivers at the head of lanes causing a slowdown.  There may be a limit to how much the police will let you do that however.

 

William Friedkin in his memoirs talks about stealing a scene in "The French Connection" where he had some stunt drivers pretend to stall out on the Brooklyn Bridge, creating a major traffic jam that he then had his actors walk through, the jam causing them to lose their suspect.  Today you could get into serious trouble for doing that.


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#12 steve waschka

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Posted 08 November 2014 - 03:19 PM

I think sometimes you become "aware". You can accept. But, never go back to being ignorant of an issue. I am aware of what you are referring. I see it in digital theaters and on my projection system at home. I don't remember it in older film systems. Doesnt mean it wasnt there.  I've experimented with what David is referring in digital shutters. I also setup an after effect that ran black space at fractions of a second to emulate a mechanical shutter. Prob is nothing I have can project a refresh rate at those speeds. But when I could get glimpses of the effect of the black space to work as it phased in and out... it did make me feel like I was reviewing 16mm on a projector. What I need to do is find an example that bugs me and shoot a similar scene in video 30fps and on film at 24 and 30. And playback on mac, dig proj and film proj. I have no footage that I know of of motion sports that do this on a film projector. But as David will tell you I also have a polarizer filtration test I've needed to do for over 2years now that I haven't done. I really think its a refresh rate / capture rate / shutter angle & type anomaly. I saw it last night in the theater. It kinda ruins the experience for me until the plot takes over and I forget about it.


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