180 degree rule

A

Andy9

Well-known member
I know it’s not a rule, I just put that so you’d click on the link out of annoyance.

I want to check I understand it correctly. Here is my understanding (Please correct me if you think I’ve got it wrong):

The amount of motion blur produced by a 1/48s shutter looks ‘natural’, ‘cinematic’… whatever, this isn’t the bit I’m interested in. This is an absolute value - the blur is the amount of movement that happens in 0.020833333333333 seconds.

At 25 fps, the equivalent motion blur would STILL be 1/48s but we use 1/50s as it’s more practical to sync with the mains electricity frequency due to problems with light flicker, banding on screens etc. if we don’t.

At 29.97 fps, we use 1/60s for the same reasons of practicality. Actually 1/48s would be more ‘cinematic’, but 1/60 is close enough and a lot easier to deal with.

So ‘Double the frame rate” is not an important ratio for calculating ‘correct’ shutter speed, it’s just an easy way to remember the standard compromises in both PAL and NTSC countries.

School me.
 
I don't believe it's that 1/48 in specific is natural or cinematic. I think that a shutter speed of half your framerate is what gives you motion blur that helps smooth your frames together in a natural way. So, when we shoot in slow motion, we still use the 180-degree rule. And no matter what your framerate is, a higher shutter angle (longer exposure) will always look smearey and a lower shuttler angle will always look strobey (although those visual effects are sometimes desired).
 
At 50fps though, I would shoot with 1/50s shutter unless I was planning to slow the footage down in post. 1/100s shutter looks stroby to my eyes when played back in real time at 50fps. So if it’s a ratio, it’s not one that holds above 30fps.
 
so, you're playing it back in a 50fps timeline? I think one issue about making this comparison is that high framerate playback has different characteristics than 24/25fps to begin with. I can't argue with your assessment if you think 1/50 shutter in 50fps timeline looks better. I can't explain it either.
 
ahalpert said:
so, you're playing it back in a 50fps timeline? I think one issue about making this comparison is that high framerate playback has different characteristics than 24/25fps to begin with. I can't argue with your assessment if you think 1/50 shutter in 50fps timeline looks better. I can't explain it either.
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Yes, playing back in a 50fps timeline. Although following my logic the correct shutter speed for filming in 50fps and playing back in real time on a 25fps timeline would still be 1/50s. I'm not sure why anyone would film at 50fps for a 25fps timeline but there you go - it should look identical to 25fps at 1/50s right?

I realise that saying 1/50s shutter at 50fps looks better to me is somewhat subjective but I don't think it's just me, I think it's pretty standard. I googled "shutter speed" with "technical specs" and didn't find much. The BBC's delivery specs ask for an "an appropriate shutter speed". Thanks guys.
 
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Hard to find literature on this exact subject. I see that the Hobbit was shot at 48fps with a 270-degree shutter angle (1/64 second shutter speed), presumably because they agreed with you that a 180-degree shutter would have been too strobey. Of course, the look of the Hobbit was widely criticized, but I think that was just because of the high frame rate itself and not the shutter angle.
 
On a related note, Kholi used to recommend shooting 1/45th rather than 1/50th for 23.976 FPS on DSLRs to improve the motion. You'll have to change the shutter speed exposure increments to 1/2 stops, and set the shutter speed to 1/45th.
 
I've been shooting with a 144 degree shutter (or equivalent if angle is not an option) for more than a decade. The 180 degree rule came about mostly for mechanical reasons for film cameras. I do not shoot film and do not feel bound by those outdated conventions. A slightly faster shutter speed produces a little less motion blur, and that looks better to my eyes.
 
Andy9 said:
Yes, playing back in a 50fps timeline. Although following my logic the correct shutter speed for filming in 50fps and playing back in real time on a 25fps timeline would still be 1/50s. I'm not sure why anyone would film at 50fps for a 25fps timeline but there you go - it should look identical to 25fps at 1/50s right?

I realise that saying 1/50s shutter at 50fps looks better to me is somewhat subjective but I don't think it's just me, I think it's pretty standard. I googled "shutter speed" with "technical specs" and didn't find much. The BBC's delivery specs ask for an "an appropriate shutter speed". Thanks guys.
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I regularly shoot in 60fps at 360 degree shutter angle. When I put it in a 24 fps timeline and play it in real time, it works great. If I want to slow it down or speed ramp I also have no issues. In fact, I kind of like the dreamy look that slow motion footage gets when you have a 360 degree shutter angle. I've even shot interviews the same way since we can record audio at 59.94p for NTSC modes. I also do some live streams where we shoot 60 fps at a 360 degree shutter angle. You keep the motion blur that people are used to seeing while also reducing strobing for quick pans or tracking shots. It is also easier to layer in graphics or other video assets at higher frame rates.

Frankly, one of my annoyances with working in NTSC is that we still don't have a standardized 48fps codec with embedded sound available on any cameras that I have used. You people are lucky with your 50fps available. I'm pretty sure that is all I would shoot in I was there.
 
cpreston said:
Frankly, one of my annoyances with working in NTSC is that we still don't have a standardized 48fps codec with embedded sound available on any cameras that I have used.
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I've had this same thought and second the motion

Personally, I think 60fps with 360-degree shutter played back in 24fps still looks a little smeary. But I'll shoot it that way if I think I'm more likely to use the footage in real-time and the slow-motion option is just a backup
 
360 degree shutter for me on a 50p timeline (PAL land).

The advantages of 360 vs 180 (all else being equal):
- Is you get more light
- No judder on fast pans or movement as all temporal information is captured (not just half)

Combining a 360degree shutter on a 50fps timeline (vs 180degree/25fps) you get twice the Temporal Resolution but with the same motion blur and less judder. You could even drop every 2nd frame in post and put it on a 25fps timeline and it would be identical to shooting 180degree/25fps.

....but it is also down to what you think looks look good. I really like the look of the doubled Temporal Resolution that you get with 360degree shutter on a 50fps timeline.

FWIW Gerald Undone did some tests on this (his summary was if deliverying on a time line > 30fps use 360degree) - Motion Blur, Shutter Speed, & 180° Shutter Angle // TESTING the RULES! - YouTube
 
jmone said:
....but it is also down to what you think looks look good.
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I think this also depends a lot on what you're filming. I virtually never drag my shutter slower than 180 degrees. But I regularly use a faster shutter, anywhere from 1/60 to possibly 1/100 in 24fps (whatever those angles are). But it definitely depends on what the action is and the desired feeling. I rarely ever deliver in a timebase other than 23.98 so I can't comment on using 360-degree shutter for high framerate projects but that sounds interesting and sorta makes sense
 
Doug Jensen said:
Is the final viewer actually watching it in a 50p environment or is it 25p or 50i?
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Yup - 50p. Even youtube etc will push out a 50 (or 60)p timeline if you feed it 50/60p.

Not many displays are left that aren't native 50 (or 60)p (or a multiple) so might as well feed it the higher framerate.
 
With YouTube now supporting AV1 streaming, I was mucking around seeing how it handled 100mbps AV1 UHD HDR 50fps upload. Not much to look at but as you can see in the stats it is a 50fps delivery from them. AV1 100 - YouTube. note: Probs looks choppy on a NTSC display (I hate the NTSC/PAL world divide).

As an aside, Turns out YouTube re-encodes as VP9 and from what I can find will only create an AV1 encode for videos with a high number of hits (I guess the makes sense in balancing the cost of streaming bandwidth vs the additional cost of creating an additional AV1 encode).
 
ahalpert said:
So, the high framerate timebase is your personal choice and not a client mandate?
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Correct. It's simply my preference of getting the "best" look I can get out of the FX6..... but a client mandate would win every time. If I was asked to produce 576/25i sure, no probs. If they left it to me, it would be targeting a frame rate that matched the intended display characteristics. These days for online viewing, it will be 50p for PAL TV's and 60p for NTSC TV's, all Phones and most PC monitors.

Keep in mind that you can always output a "traditional" (25/30p) version in post with no issue if required for some odd compatibility reason, so you might as well capture in the higher frame rate (if you don't mind the bigger files). Different story if you want 24p "film" but I'm not sure this is a great option if the viewing is to be done on a digital displays as it is both low temporal resolution, and few displays are going to auto switch to 24hz so you will end up with a pull down judder issue. It is a "look" however.
 
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