HFR (120, 240, 480, 960) and 180 degree shutter rule?

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Petrovich

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Not entirely sure where to post this question so maybe someone can answer here or make a suggestion...

I'm starting to explore Sony's HFR capabilities (specifically with RX10ii and RX100iv that I just acquired. I'm a bit confused about the 180 degree shutter rule application when shooting in HFR modes. If I want to, for example, shoot at 240fps/24p... should I be looking at 1/500 shutter (using the Manual mode to set exposure parameters)? Same for the other frame rates... 480fps/24p would then demand the 1/1000 at that point, and then 960/24p would then demand 1/2000, which could obviously be very limiting... what am I missing?

I guess the confusion is because Sony is doing the conversion in camera to adapt HFR footage to 24p (for that cinematic look, that is) and I'm just drawing a blank here.

Any other suggestions or resources on shooting in HFR that you may share would be appreciated! Thanks in advance!
 
The 180 degree shutter "rule" is based on 180 degrees being the minimum shutter speed equivalent possible with a simple rotary mechanical shutter, it therefore applies at any capture frame rate regardless of display rate (up to you if you want to apply the rule).
 
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Petrovich said:
If I want to, for example, shoot at 240fps/24p... should I be looking at 1/500 shutter (using the Manual mode to set exposure parameters)? Same for the other frame rates... 480fps/24p would then demand the 1/1000 at that point, and then 960/24p would then demand 1/2000, which could obviously be very limiting... what am I missing?
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The point of the "rule" is to make motion look realistic. For that to happen, you need a certain amount of blur in each frame. When you're shooting at 24fps, that turns out to be around 1/48 of a second exposure. That makes a certain amount of sense, yes?

But what happens as you decrease the exposure time? The amount of blur in a given frame goes down. When you get past about 1/125, there's very little blur. When you get to 1/250, hardly any even with a very fast moving subject.

What I'm getting at here is that as you increase your fps, you decrease the "need" for the 180 degree shutter rule. And at the same time, using the 180 degree shutter costs you a stop of light, so you need brighter lights, which typically means heavier, bulkier lights, which can be a PITA.

So unless I'm shooting in the 24-60 fps range, I tend to use 360 degree shutter angles instead of 180 degree shutter. I typically want the greater exposure at the expense of that tiny amount of motion blur. But that might just be me, and it sure as heck depends on what you want out of your footage, and what your subject is. There's no single answer that's alway correct for all circumstances; clearly YMMV.
 
wound't the blur still show once conformed to 24p?

wound't the blur still show once conformed to 24p?

Bruce Watson said:
What I'm getting at here is that as you increase your fps, you decrease the "need" for the 180 degree shutter rule. And at the same time, using the 180 degree shutter costs you a stop of light, so you need brighter lights, which typically means heavier, bulkier lights, which can be a PITA.
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Bruce - thanks. I understand the 180 rule (or so i think!) and it's application. I guess what I'm wondering is this: even at such crazy FPS as 480/960 there is, presumably, some motion blur. Tiny as it might be looking at a single frame, when spread across all the frames necessary to conform to 24p, it will all add up to the "noticeable" blur that you'd expect to see when shooting native 24p and following the 180 degree shutter rule by keeping your shutter speed at 1/50. Doesn't that seem logical? Thanks again!
 
You can't have a greater than 360 degree shutter on a single exposure. So for example 1/50th second (360 degrees) is effectively the minimum speed you can shoot at 50fps. Like Bruce says, above 60 fps (well, I'd say 100fps) you're better shooting 360 degrees to maximise the light. Or am I missing the point?
 
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Rainer said:
You can't have a greater than 360 degree shutter on a single exposure. So 1/50th second (360 degrees) is the maximum speed you can shoot at 50fps. Like Bruce says, above (well, I'd say 100fps) you're better shooting 360 degrees to maximise the light. Or am I missing the point?
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This might need to be clarified as you can most certainly shoot above 1/50th second when shooting 100fps on a digital camera. Another rule of thumb is to put the shutter speed at the HFR. So 240fps would have a 1/250th second shutter. On the RX10 MKII the shutter is set to a minimum of the HFR so you can not go below your framerate. If in doubt test test test and get firsthand information rather than internet info.
 
Petrovich said:
I guess what I'm wondering is this: even at such crazy FPS as 480/960 there is, presumably, some motion blur. Tiny as it might be looking at a single frame, when spread across all the frames necessary to conform to 24p, it will all add up to the "noticeable" blur that you'd expect to see when shooting native 24p and following the 180 degree shutter rule by keeping your shutter speed at 1/50. Doesn't that seem logical?
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No, it does not seem logical. But you don't have to believe me. It's really easy to test it out yourself and make your own decisions based on your own results. So shoot some 480 fps footage at 1/1000, and shoot some at 1/500. Play it back at whatever speed you want, hopefully on as big a screen as you have available. Tell us what you see.
 
That's the idea, thanks! I will test this coming weekend and if there's anything interesting to report (namely, seeing any meaningful differences in the amount of motion blur) I'll be sure to share. Just need to think of something that's easily measurable/repeatable between different shots.
 
Try a fan or a bicycle upside down with the tire spinning.

FWIW, higher shutter speeds/lower shutter angles for HFRs have always looked better for me. (Have shot hundreds of hours of slow-motion...mostly sports.)
 
If the footage is 100% going to only be used for slo-mo then higher is often better if you have the light. If you are indoors then the never ending battle between light and shutter will continue...
 
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