Shutter speed for 60p

[Nate Haustein]

When shooting 60p, (and planning on delivering as 30p), would one use 1/120 shutter speed? Or would 1/60 give more natural motion? I don't particularly like the look of typical 60p motion blur, but I do like the flexibility of 60p in post production for slow motion. Thoughts and personal experiences?

[Paul Kellett]

I'm having exactly the same thoughts, i'm in pal land though.
I've done some experimenting.

1.Shoot at 50p 1/100, rendered to 50p, looks ok.
2.Shoot at 50p 1/100, rendered to 25p, (so i'm left with 25p 1/100) too much judder in pans and movement (me waving my arms).
3.Shoot at 50p 1/50, rendered to 50p, looks ok.
4.Shoot at 50p 1/50 rendered to 25p,(so i'm left with 25p 1/50) looks ok
5.Shoot at 25p 1/50, rendered as 25p, looks ok, looks exactly the same as 4.
6.Shoot at 50p 1/50, slowed to 50% in edit, rendered to 25p, looks ok
7.Shoot at 25p 1/50, slowed to 50% in edit, rendered to 25p, too much judder

So, i think 50p 1/50 is good for lots of adjustment in the edit.
Also, 1/50 shutter is obviously going to let in more light than 1/100.
50p 1/50 vs 50p 1/100 regarding blur, i'm struggling to see much difference in blur when rendering out to 50p.

If someone can convince not to shoot 50p 1/50 other than breaking the 180 rule, then i'm listening.

All the above shot at 4K so that also brings the cropping advantages.

Paul.

[Nate Haustein]

Thank you for your detailed answer, Paul. Your examples 4 and 6 are the ones I see myself implementing the most, but I definitely don't want 2 to happen. If there are scenarios where I KNOW I'll be using slow motion, I think it makes sense to quickly up the shutter to 1/100, but since much of what I'll be working on is run-n-gun, it doesn't make sense to jeopardize the 90% of the footage that isn't slow mo just for slightly better looking slow mo 10% of the time.

[Ron Evans]

I shoot at 1/60 both for interlace and 60P as I shoot in the theatre and need the extra light. My understanding of the 180 rule was it was set to ensure that for slow frame rates the image was not so sharp as to emphasis the judder of the slow frame rate. With 50 or 60 fps there are enough frames to remove this issue and then it comes down to exposure.

[Paul Kellett]

Originally Posted by Nate Haustein

If there are scenarios where I KNOW I'll be using slow motion, I think it makes sense to quickly up the shutter to 1/100,

When shooting at 50p but rendering out to 25p ? Then you will get the judder if you slow the 50p 1/100 in post.

Paul.

[Paul Kellett]

Originally Posted by Ron Evans

I shoot at 1/60 both for interlace and 60P as I shoot in the theatre and need the extra light. My understanding of the 180 rule was it was set to ensure that for slow frame rates the image was not so sharp as to emphasis the judder of the slow frame rate. With 50 or 60 fps there are enough frames to remove this issue and then it comes down to exposure.

Thanks for the explanation Ron.

Paul.

[Adam Grunseth]

The 180 degree shutter rule came about in the early days of motion film acquisition.

Film costs money. So, there is a financial drive to use as little film as possible. One way to accomplish this is shooting at a lower frame rate- if you shoot at 10 frames a second, you use less film compared with shooting at 100 frames a second. The problem is, of course, that two low of a frame rate will look more like a fast slide show than a moving picture.

The problem for early motion picture pioneers faced was a way to figure out the lowest possible frame rate that we could still perceive as smooth motion. Ultimately, they landed at 24 frames per second, which became the standard for motion picture film.

However, even at 24 frames per second, things had a bit of a rapid-slideshow feel to it. You should be able to try this yourself by shooting at 24fps with a 1/24" shutter speed. It doesn't look good.

To solve this problem, a shutter speed of twice the frame rate was used, or a 180 degree shutter angle. So film at 24 fps had a 1/48" shutter. When projected, each frame would be double flashed by the shutter on the projector. The result of all this was a motion cadence that was similar to 48 frames per second. But, it is all just a trick to make our brains interpret what we are seeing as smooth motion.

For the sake of this discussion, I'm going to totally skip over interlaced formats and how interlacing impacts perceived motion rendering.

Once you are shooting at a frame rate of 50 fps or 60 fps, if you want the motion to appear similar to that of 24 fps or 30 fps material, shooting at shutter speed that matches the frame rate is the way to go. For 100 years we have been trained that the motion rendering of a shutter speed between 1/48" and 1/60" looks normal. Increasing that, the footage will have a "sped-up" feeling to it, which is fine if that is what you are going for.

The exception to this is if you are shooting high speed for slow motion. If you are shooting at 60 fps, with the intent of doing slow motion playback at 30 fps, you would want to use a 1/120" shutter speed. When slowed down, this becomes a 1/60" shutter speed, creation natural looking motion a 30 fps. Everything is smooth and looks right, it is just moving slower.

[Paul Kellett]

That is a great explanation, thanks Adam

Paul

[Ron Evans]

Just to add a little. Before sound the frame rates were even lower but to get acceptable sound from the optical sound track 24fps was chosen. The other thing as noted is the image is projected twice so the refresh rate was 48 images a sec as mentioned about the lowest one would view the image as "real" rather than a slide show. Some view 48fps as the choice the engineers would have made but the accountants won !!! Of course with video one is dependent on the refresh rate of the display ( TV ) which will be either 50 or 60 for most people unless they have a more modern TV with higher refresh rates like 120hz etc, to show 24P on these sets one of course has to match somehow the refresh rate and hence 2:3 pulldown for at least 60hz. This approach works for LCD as well as interlace CRT as then the film frame would be displayed as fields with same pulldown. Show the first frame twice then the next 3 times. That way the sum will be 60. For sets with a 120hz refresh then this cadence is not needed and the TV is able to display each frame 5 times and get true 24fps display however of course the flicker rate is different to a 2 blade film projector. My Super8 film projectors have a 3 blade and a 5 blade shutter for projection. The other issue to look at is the motion blur during exposure of each frame. A slow shutter will blur the image more than a fast shutter depending on subject motion of course. Too fast a shutter will make the judder more obvious as I mentioned. Too slow and the image may be totally blurred, once again the compromise was to use the 180deg shutter angle of the film camera.

[Rainer Listing]

And just to add more from the capture end: 180 degrees is the theoretical maximum opening for a standard rotary focal plane (half-moon or butterfly) shutter in a film camera. For some reason this seems to have become bastardized into the "180 degree rule" we have today. In fact most of these film cameras shot at less than 180 degreesto compensate for frame slap, the angle commonly was adjusted smaller if there was enough light, and crystal synch on some popular cameras reduced the maximum angle to around 140 degrees. No-one seemed to notice or mind. With video we have no such limitations.Strobing isn't an issue at 120 degrees, hand held you're less susceptible to shutter blur and you may find your image looks better. Waltzes with a stable camera at dim wedding receptions look fine at 360 degrees. The important thing is to be aware of what you're doing and how shutter angle affects your image rather than blindly following a "rule".

[John McCully]

Originally Posted by Adam Grunseth

For 100 years we have been trained that the motion rendering of a shutter speed between 1/48" and 1/60" looks normal. Increasing that, the footage will have a "sped-up" feeling to it, which is fine if that is what you are going for.

Point of clarification: the cinema industry might well have been producing movies shot at 24p shutter speed between 1/48" and 1/60" for 100 years but I for one have not been trained for 100 years (sometimes I do feel that old) to believe that to be normal, and certainly neither have my grand-kids and their generation. If you can point me to a study that supports that notion, assuming 'we' to mean the population at large, I would be most interested. Interestingly, according to a recent study (I shall post a reference when I can locate it again) those who have played video games prefer higher frame rates and have no clue about shutter speed whatsoever.

Hollywood type movies shot and viewed at 24p account for a smaller and smaller percentage of moving pictures 'we' watch these days, while 24p and the 180 degree shutter rule are becoming less relevant with each passing video clip we view, in my opinion.

Now, if you ask a movie critic you will likely get a very different answer.

[Rainer Listing]

I'd also be interested in that study. My recollection is the 180 degree rule in cinematography was about maximizing light, if there was any concern about motion blur it mostly was about how to avoid it. Once reflex shutters became available around the early 1960's, Hollywood was happy to shoot up to 270 degrees. I have no doubt they would have used 360 degrees had it been possible.

[Brian Drysdale]

Motion blur has been an part of cinematography since the beginning, however, 210 degree shutter is about the max I've heard off, the Mitchell workhorses had 175 degree shutters

Camera movement is common and fast shutter speeds will cause problems with stuttering moves at the standard frame rates,

Higher frame rate productions are different, because you;re increasing the temporal resolution compared to 24 fps .productions.

[Steven Davis]

Originally Posted by Adam Grunseth

The exception to this is if you are shooting high speed for slow motion. If you are shooting at 60 fps, with the intent of doing slow motion playback at 30 fps, you would want to use a 1/120" shutter speed. When slowed down, this becomes a 1/60" shutter speed, creation natural looking motion a 30 fps. Everything is smooth and looks right, it is just moving slower.

So if I'm shooting 60 fps and want to only slow certain parts down, should I switch between 1/120" and back to 1/60 only on parts I want to slow down? Or just lay down at 1/120" and everything will be peachy.

[Rainer Listing]

Originally Posted by Brian Drysdale

Motion blur has been an part of cinematography since the beginning, however, 210 degree shutter is about the max I've heard off, the Mitchell workhorses had 175 degree shutters

My recollection, later large format Mitchells typically were used at 200 degrees, Earlier Arri's claimed to be 180, but were actually only 175. But I could be wrong, long time ago, don't suppose it matters too much now. One thing about the Mitchell, you could change speed while shooting.
As for 60p, if you're following it blindly, keep following the 180 degree "rule", i.e shoot at 1/120th. The 180 degree rule mostly is a reasonable rule of thumb. Any experienced cinematographer won't be religiously bound by it. They'll aim for a particular result, taking into account camera movement, subject movement, available light. If in the particular scene you're shooting at 60 fps you prefer the look at 1/60th when shown at 30fps, that's what you use, same goes for 1/120th.