GH4 Proper shutter angle for various VFR slow motion speeds?

F

filmguy123

Veteran
The GH5 should make this easier with a locked 180 degree shutter angle... in the meantime:

I know 1/50 (well, 1/48 technically) is where we want our GH4 shuttle angle set to for 24fps.

But what about when filming VFR @ 36fps? 48fps? 72fps?

Would it be 1/72, 1/110, 1/140-1/150 (respectively)? Why or why not?

I notice often times the camera just leaves the shutter angle set to 1/50 when I change to different VFR modes, and occasionally forces a bump up to 1/60 or 1/80.

How does this work, how is it calculated in respected to VFR, and what are the image effects in regards to leaving the shutter speed only fast enough for 24fps playback instead of upping the shutter alongside the overcrank rate? I know it will equate to motion blur, but in terms of slow motion, might the extra blur be more desireable or have a different aesthetic than leaving it locked to 180 shutter?

And/or does that depend on the type of slow motion shot (ie a 72fps atheletic shot VS a 48fps portrait shot of someone smiling) - might more motion blur be ok or desired in a portrait style shot, for example?

Thanks for the help on understanding this, as well as the technical and creative implications!
 
Shutter should ideally be double the framerate (that is 1/48 for 24, 1/60 for 30, etc) otherwise you'll get too much motion blur, simple as that. This is why slow motion eats so much light, since if you are really over cranking it your shutter speed is gonna be up in 1/200-1/300 range when we are looking at the VFR on the GH5. The shutter obviously can't be slower than the framerate, so if you have it set to 1/50 and set the VFR to 60fps, it will force it to 1/60 at a minimum since each frame is being captured faster than 1/50th of a second.

A 180 degree shutter angle always keeps this ratio which makes it a bit simpler (and the GH4 can also do shutter at angle instead of sec, this isn't exclusive to the GH5)

If you want more motion blur in your slow motion for a specific effect, than sure you can keep the shutter speed slower to achieve that. But if you just want normal slow motion that you are cutting with regular footage, then you'll want to maintain that 180 degree shutter angle so you don't cut from a normal shot with normal motion blur to a slow motion shot with too much motion blur.
 
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To me shutter speed is just motion blur. If you want the motion blur associated with say 30p then you can use that if you are shooting 60P. That way you can edit and output in either 60P or 30P from the timeline. However if you use a really fast shutter speed at a slow frame rate then the images will be very sharp and judder becomes more obvious. Hence the shutter angle rule. I see it the other way around as do not use a shutter speed faster than you need for motion blur especially for slow frame rates. At 60P you likely will not have a problem as judder will not be obvious just because of frame rate. Of course you cannot shoot slower than the exposure rate so at 180fps you will have to be at 1/180 or faster. Most video cameras shooting 60P in auto default to 1/60 and I shoot in the theatre with my video cameras whether 60i or 60P at 1/60 on all of them as it gives me a little more exposure range rather than using gain. No real fast motion in the theatre so not a problem. Outdoor in good light for sports then of course I would go faster.
 
Ron Evans said:
To me shutter speed is just motion blur.
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It also has a large impact on light gathering.
If you want the motion blur associated with say 30p then you can use that if you are shooting 60P. That way you can edit and output in either 60P or 30P from the timeline. However if you use a really fast shutter speed at a slow frame rate then the images will be very sharp and judder becomes more obvious. Hence the shutter angle rule. I see it the other way around as do not use a shutter speed faster than you need for motion blur especially for slow frame rates. At 60P you likely will not have a problem as judder will not be obvious just because of frame rate. Of course you cannot shoot slower than the exposure rate so at 180fps you will have to be at 1/180 or faster. Most video cameras shooting 60P in auto default to 1/60 and I shoot in the theatre with my video cameras whether 60i or 60P at 1/60 on all of them as it gives me a little more exposure range rather than using gain. No real fast motion in the theatre so not a problem. Outdoor in good light for sports then of course I would go faster.
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Note that the amount of desired/acceptable blur for 60fps played back at 24P is different than for 60fps played back at 60P. When using high frame rates for slow motion, it is important that the shutter speed is such that it creates a matching motion rendition to the "base" frame rate. That's definitely NOT going to be the case if the shutter is open for the entire frame duration.
 
So shooting 60p slow motion over 24ps at 1/60 shutter is the equivalent of 360 shutter angle, correct?

When motion is played back in slow motion, is the effect less noticeable than 360 shutter angle at 24fps?

I have shot stuff at 60p 1/60 shutter and it has seemed fine, but shooting 24fps at 1/24 is a blurry mess. Why?
 
joe12south said:
It also has a large impact on light gathering.

Note that the amount of desired/acceptable blur for 60fps played back at 24P is different than for 60fps played back at 60P. When using high frame rates for slow motion, it is important that the shutter speed is such that it creates a matching motion rendition to the "base" frame rate. That's definitely NOT going to be the case if the shutter is open for the entire frame duration.
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Yes as I mentioned I use 1/60 so that there is more light gathering rather than use gain in my instance. There is no shutter in modern video cameras only the time the sensor gathers light, hence shutter speed is more appropriate. Doesn't matter what the frame rate the motion captured in the time the sensor is sampled is the same. Slow shutter speed and there will be more blur of the motion being captured, faster shutter speed and the motion will be frozen at that speed just like taking a still picture. They are after all a series of still pictures. If you want to slow down 60P to 24 then as you say the motion blur needs to be for 24p or 1/48 if it is faster then judder will be more pronounced if there is motion in the image if it is slower then motion blur will eventually degrade the image to mush !!! Shutter speed is more critical for the slower frame rates because of judder and the need to mask the slow frame rate. Once you move up to 60P the frame rate itself is sufficient and shutter speeds can be higher though 1/60 is fast enough for most unless one wants a really sharp image for faster motion.
 
Ron Evans said:
There is no shutter in modern video cameras only the time the sensor gathers light, hence shutter speed is more appropriate.
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Whether the shutter is physical or electronic makes no difference to the original topic. If you're shooting VFR, setting a shutter ANGLE is the way to go, as it removes you from having to remember to change the shutter SPEED when you change rates. If my base rate is 24P, it doesn't matter if I'm shooting 24fps, 60fps, or 180fps – the shutter angle stays at 180º.

This is one of those brilliant little touches that keeps me using the GH-line even when this camera or that camera has better color, or low light, or whatever.
 
joe12south said:
Whether the shutter is physical or electronic makes no difference to the original topic. If you're shooting VFR, setting a shutter ANGLE is the way to go, as it removes you from having to remember to change the shutter SPEED when you change rates. If my base rate is 24P, it doesn't matter if I'm shooting 24fps, 60fps, or 180fps – the shutter angle stays at 180º.

This is one of those brilliant little touches that keeps me using the GH-line even when this camera or that camera has better color, or low light, or whatever.
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This!
 
joe12south said:
Whether the shutter is physical or electronic makes no difference to the original topic. If you're shooting VFR, setting a shutter ANGLE is the way to go, as it removes you from having to remember to change the shutter SPEED when you change rates. If my base rate is 24P, it doesn't matter if I'm shooting 24fps, 60fps, or 180fps – the shutter angle stays at 180º.

This is one of those brilliant little touches that keeps me using the GH-line even when this camera or that camera has better color, or low light, or whatever.
Click to expand...

If you are shooting for 24fps I do not think the shutter speed/angle is changing with VFR ? You want the same motion blur to match the esthetic. In 24fps VFR does the GH line stay at its base rate shutter speed, 1/48 ? I assume that if the shutter angle changed as you shot 60fps to match the frame rate ( 180 rule it would be 1/120sec ) the image would have less motion blur and when slowed down would be an obvious change when mixed with normal 24fps video. Not what you want. I really shoot with video cameras and have ordered a GH5 for it capabilities. I think you may have misunderstood me a little. I shoot 60i and 60P at 1/60 which is not the rule I know if you are a traditionalist shooting film at 24fps. 60fps is fast enough to avoid judder and give a smooth image so the shutter speed is a way of taking advantage of light. Not as easy to do at 24fps. At 24fps if you set shutter speed too fast then the image is too sharp and judder will become very obvious. Too slow and the motion blur is too much and the image turns to mush, hence the rule. As you can tell I am not a fan of slow frame rates and shoot all the time at 60 but I do understand the whole issue of frame rate and shutter speed. I am not a young guy and started shooting film in the early 1960's moving from Super8, 16mm then into video. My goal is different to someone who wants the film look as I strive for "being there" look or looking through a window. High resolution and high frame rates. Reason for the GH5 is UHD 60p with interchangeable lenses if you had not figured that out !!
 
Ron Evans said:
If you are shooting for 24fps I do not think the shutter speed/angle is changing with VFR ? You want the same motion blur to match the esthetic. In 24fps VFR does the GH line stay at its base rate shutter speed, 1/48 ? I assume that if the shutter angle changed as you shot 60fps to match the frame rate ( 180 rule it would be 1/120sec ) the image would have less motion blur and when slowed down would be an obvious change when mixed with normal 24fps video.
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Sorry, Ron, I'm having a little trouble following you here, but if I understand what you're asking, then no, when shooting for slow motion, keeping the same shutter angle does not make the blur look like an "obvious change", it's actually the opposite. 60fps footage played at 24P needs a shutter speed of 120/sec (180º) to match the intercut footage shot at 24fps with a shutter speed of 48/sec (180º). If you were shooting at 180fps, you would need a shutter speed of 360/sec (180º). All of those settings will yield the same amount of motion blur.

If you are shooting 60fps for 60P, then all of those guidelines go out the window. There is no real consensus about what looks "right". What impressions we do have come from watching news, live sports and soap operas, so there's definitely no expectation of what looks "dramatic" or "cinematic." I personally don't like the look for narrative work, but if I did, I would agree that I would likely use a wider angle than 180º.

PS. "Judder" isn't really a good term to describe the staccato motion rendering of fast shutter speeds. Judder typically refers to an artifact of film projection or of the telecine process (2:3 pulldown, converting 24P into 29.97P.)
 
I wanted to find out if with a base rate of 24fps in VFR does the GH actually change the shutter speed. I would like to know , that is all, as to me it should stay at the base rate to maintain image blur consistent. Remember the camera is taking a series of still images all the time we just view them as video. If you shoot a still image with a 1/48 shutter speed it will look different to a still with a shutter speed of 1/360. May not be to too different if the subject is a chair but will be different if it is a person moving. One will be a lot sharper than the other. Slowing it down will make no difference to how we see that single frame. It depends on how the slowdown will be done. If one is using a piece of software to slow down a normal rate file then the file needs to have sharp edges for the software to key on to create the extra frames, then I can understand needing a sharper image from faster shutter speed. However I was under the impression that the internal VFR was actually recording images at the higher rate but playing them back at the base rate, which is why on some cameras there is a buffer limit before the file is written to memory. That is why I would have assumed the shutter speed for these extra frames had to be at or close to the base rate otherwise those slowed down frames would be very sharp in comparison to the normal speed frames. Maybe that is what one wants from a slow motion file or what is needed to make it look good rather than the normal motion blur. I can see that if there is fast motion that would be a problem for 24fps then shooting at a higher speed with a faster shutter would be needed to create a slow motion 24p end file. This is often done in feature films I know when the action would just be too fast for 24p.

Yes maybe I should have used cadence rather than judder though I find both annoying to my old eyes.
 
Ron Evans said:
I wanted to find out if with a base rate of 24fps in VFR does the GH actually change the shutter speed. I would like to know , that is all, as to me it should stay at the base rate to maintain image blur consistent. Remember the camera is taking a series of still images all the time we just view them as video. If you shoot a still image with a 1/48 shutter speed it will look different to a still with a shutter speed of 1/360. May not be to too different if the subject is a chair but will be different if it is a person moving. One will be a lot sharper than the other. Slowing it down will make no difference to how we see that single frame. It depends on how the slowdown will be done. If one is using a piece of software to slow down a normal rate file then the file needs to have sharp edges for the software to key on to create the extra frames, then I can understand needing a sharper image from faster shutter speed. However I was under the impression that the internal VFR was actually recording images at the higher rate but playing them back at the base rate, which is why on some cameras there is a buffer limit before the file is written to memory. That is why I would have assumed the shutter speed for these extra frames had to be at or close to the base rate otherwise those slowed down frames would be very sharp in comparison to the normal speed frames. Maybe that is what one wants from a slow motion file or what is needed to make it look good rather than the normal motion blur.
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Okay, I understand what you're asking now, but the answer is the same. Yes, the GH4 is actually recording more frames, and if you are using the shutter angle feature, the GH4 changes the shutter speed when you change VFR rates. If you want your slow motion footage to "fit" with your normal speed footage, the shutter needs to stay open for half of the exposure time, not half of the base rate's exposure time.

I think what you're missing is that the goal when shooting slow motion is to capture something happening faster than normal, render with motion characteristics that look normal. If you did not increase the shutter speed, those actions would simply be too blurry to match expectations. You could possibly get away with it if ALL of the action is very slow, but as soon as something moves quickly, the blur would give it away. I'm having a difficult time finding the correct words to explain this, but if you just shoot both ways, it's very easy to see in practice.

It's worth noting that the same methodology works if you are going to synthetically slow the motion in post. Let's say I shoot at 60fps because that's as high as I can (camera, light, whatever) but I know I'm going to drop it into a 24P timeline and slow it to 240fps in post. In this case, I should set my shutter speed to 480/sec, not 120/sec and definitely not 48/sec. You begin to see why high frame rates gobble up the light.
 
I too am stuck on this as to me blur is shutter speed dependent only not frame rate. They are all still images one after the other no matter how many there are in a second. Blur is governed by just how long the shutter is open to expose for the frame ( and consequently blurring the motion occurring during this time ) and nothing to do with the frame rate. The motion associated with frame rate does impart the esthetic to the video and I agree that 24fps gives very different look to a high frame rate. I can see that one needs to use a shutter speed appropriate for the frame rate but above 60p there is little need to go much above 1/60 if you do not need to based on what is being filmed. At 1/480 you will clearly freeze most images with no blur at all. Yes I do understand that to get clean slow motion one does need a clean source and a fast shutter speed does this. However the outcome does not have a 24fps motion blur it has the blur of whatever the shutter speed was at which it was shot. It doesn't get blurry because it is slowed down. Also the playback has a slow motion esthetic also not the normal 24fps look. Just happens to be played back at 24fps the motion is much smoother but slower. I just do not see the need to create an exposure issue in use of high shutter speeds if they are not needed. Yes I do understand that there is a difference between a person walking towards me that I want in slow motion and a fast car crashing into a wall that i want to slow down. My comments are purely associated with motion blur and shutter speed. In that regard then one needs to decide how fast a frame rate is needed for the action and also shutter speed for desired effect and that may not be the 180 rule. I accept letting the camera do what you say will work but also may not be the optimum.

That's fine . Will play when I get my GH5 as my range is limited on the cameras I have now.
 
Let's use the example of someone walking towards you. Their arms are gently swinging.

24fps are shot for 24P playback with a shutter speed of 1/48th of a second.

Now, we want to intercut a slow motion version of this, and we want it to "feel" like it fits. So we shoot it at 60fps, but we accidentally leave our shutter speed at the same 1/48th of a second. Wait, the normal speed footage looks good, but the slow motion doesn't look right at all! The subjects arms are all blury, but their arms aren't moving quickly, they're swinging slowly. Why are they blurring?

See what I mean now? We expect that the arms would blur in one instance, and not the other, because the playback speed of the subject's arms has changed. We only expect things that are moving fast in playback speed to blur. We expect the same relative amount of motion blur, not the same absolute amount of motion blur.

The wonderful thing is that simple math takes care of this for us, and using shutter angle makes it even easier. Pick the angle that gives you the look you want at normal speed and then forget about it, knowing that your VFR footage will be automatically adjusted to match.
 
Ron, I'm certainly no expert, but I THINK the thing you're overlooking is that motion blur is dependent on frame rate in the sense that for every frame exposed within a second it is exposed at a specific duration dictated by the frame rate.

At least in my mind, if regular 24fps footage exposes 24 separate frames over the span of one second, each frame is exposed for 0.04166 seconds. (1 second divided by 24 frames)
And if 60fps footage exposes 60 separate frames over the span of one second then each frame is exposed for 0.01666 seconds. (1 second divided by 60 frames)

This obviously isn't the case when taking stills as the shutter speed is the only thing dictating the duration of exposure. I THINK that is possibly the difference in how your viewing it. But because moving footage has its frames' duration of exposure dictated by how many frames it needs to expose per second, the shutter speed would need to adjust with the frame rate to maintain the similar motion blur.

But I could be talking out of my ass :)
 
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