7D - slomo pretest question

W

WhiteMonkey

Well-known member
This might save me some time if anyone's got the knowhow to set me straight.

I've got a JVC GY-HD100U I'm using to shoot 720P 24P as a master shot during some choreographed fights. I'm using two 7D's to shoot 720P 60P footage as B and C roll.

What shutter speed on each camera would be best to catch the action and mix it in editing?

Would I be better off matching an 180 degree shutter between the cameras or is my motion blur in the 60P not going to be the same when I conform the 60P footage to 24P because of the additional frames?
 
I don't think I was clear. I'm guessing but the motion blur is not going to match because of the frame rate and there is little I can do to match the 180 degree shutter on the HD100U.

I can however speed it up and get a more strobe-like effect like what I'm expecting from my tests on the JVC.

So does anyone have any experience with this? If not I'll post some results. I know there's some geeks and nerds around here like me who'd be interested in a scientific test concerning motion blur and matching different frame rates while using slow motion.
 
It's just that the motion blur is going to be different if the shutter speed is different. I now think that by setting them both to 1/125 the motion blur captured will be the same, once 24 times a second or once 60 times a second. Is that right?

I'm going to run some tests. Thanks for your input. I'll let you know what I find.
 
if you set them both at 1/125th, the 60p footage will look normal, but the 24p footage will look strobey, adrenalitic, like the beginning of saving private ryan

if you want to match, take wjm's advice

when you conform your 60p footage to 24p, you're stretching time; it's as if things were moving slowly and you were recording 24p; and in that "stretched time" universe in which you record 24p, you want 1/50s shutter, i.e. keep the 180º shutter rule; in the regular world, before conforming your footage, that means 1/125s shutter

edit: imagine you shoot a toy train moving along; when you see the final video, you can't know if that's a train moving slowly and being captured at 24fps, or a train moving fast and being captured at 60fps; in order to have both kinds of footage look the same you need 1/50s footage in the first case and 1/125s on the latter, otherwise motion blur (how much the train moves while the shutter is open taking one frame) and strobing (how much the train moves while the shutter is closed between two consecutive frames) will be different

just two more things:
* if this is not outdoors, avoiding flicker from your lights is more important than keeping 180º shutter
* check this out (I still can't believe they chould film all that in 4 hours!!):
http://www.vimeo.com/16403033
 
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Norman, for a fight scene, the 'strobe' or staccato look of a faster frame rate is not such a bad thing (eg: Saving Private Ryan).

My suggestion would be to shoot the 24p stuff at about 1/100th and the 60p stuff faster - maybe 1/200th.
 
We shoot 24p at 1/50 and 60p at 1/125. To us it looks more correct. As stated, since you are slowing down the actual playback of the 60p, having the motion blur being the same does not make sense, because it won't be the same since the speed of movement is slower.

In other words, look at it with this theoretical example:

If something is moving at speed X and you record at 30p let's say, let's assume the motion blur takes up 20% of the edges of that object. (say 1/60)

Now, if you recorded that at 60p at 1/60 and slowed it down, to 30p, the object is moving at X/2 but the motion blur is still taking up 20% of the object. This is because the frame times are exactly the same, you are just recording more of them.

This is why the rule we follow is to shoot as close to the same RELATIVE shutter speed in whatever mode. basically, this means same ratio. So if you are shooting 24p and using 1/48, you can easily tell that for 60p, you need 1/120 (or whatever close your camera can do).
 
MOTION TEST
HD100U settings: wide angle adapter
720P 24P, cine-gamma, 180 degree shutter 1/48
720P 24P, cine-gamma, 1/60
720P 24P, cine-gamma, 1/120
720P 24P, cine-gamma, 1/250
720P 24P, cine-gamma, 1/500
720P 24P, cine-gamma, 1/1000
7D settings: Canon 50mm 1.4
720P 60P, Marvels 3.3, 1/50
720P 60P, Marvels 3.3, 1/60
720P 60P, Marvels 3.3, 180 degree shutter 1/120
720P 60P, Marvels 3.3, 1/250
720P 60P, Marvels 3.3, 1/500
720P 60P, Marvels 3.3, 1/1000

These are the shots I'm going to attempt to give me a chance to mix and match. I'm having a hard time believing anyone right now. The math isn't adding up for me.

I do have another question. Is the aperture setting going to influence the Motion Blur? I plan on sticking to F4 while shooting the action.
 
aperture doesn't affect motion blur, it only affects general sharpness and depth of field

if you want the strobey look, use a sharper shutter (e.g. 90º), but make that consistent through your regular and overcranked takes; if you mix 24fps at 1/125s with 60fps at 1/125s, your regular shots will look sharp and strobey, but your slow-mo will look (comparatively) softer
 
I'm not sure why the math is being so complicated, it really is pretty straightforward. I think you need to wrap your mind around motion blur. It is caused by two things only, the speed of an object moving across the sensor, and the exposure time. That's it. Aperture has nothing to do with it at all.

If you shoot 30p at 1/60 and 60p at 1/60 then anything moving across the frame is going to have the same motion blur when played back at 30p and 60p respectfully. If the first frames were lines up, every frame of 30p would look exactly the same as every other fram from 60p. You are just shooting another frame in the time when the 30p would be doing nothing.

The problem is, when you take that 60p and play it back at 30p, anything moving across the sensor will be moving at half the speed as it looks in the 30p shot. However, you still have the same exact motion blur as if it were moving twice the speed. This is wrong. You need that motion blur to match what it would look like if the object was moving at that speed. What you will see is more motion blur that just makes the images look more smeary, and not what you want.

This is why no matter what speed you shoot in, you shoot with the same ratio of frame exposure to frame rate. As long as you keep that consistent, the motion blur will look correct.

Of course, I encourage you to test it, because that is the best way to learn, I'm just putting this here for the benefit of others as I am sure many people have this question.

On my AF100, I shoot everything in 180d mode (180 degrees) which comes from the film world, and it's basically an exposure time of half the frame rate (assuming the frame rate is 360 degrees). All my slow motion shots look fantastic like this.
 
WhiteMonkey said:
MOTION TEST
HD100U settings: wide angle adapter
720P 24P, cine-gamma, 180 degree shutter 1/48
720P 24P, cine-gamma, 1/60
720P 24P, cine-gamma, 1/120
720P 24P, cine-gamma, 1/250
720P 24P, cine-gamma, 1/500
720P 24P, cine-gamma, 1/1000
7D settings: Canon 50mm 1.4
720P 60P, Marvels 3.3, 1/50
720P 60P, Marvels 3.3, 1/60
720P 60P, Marvels 3.3, 180 degree shutter 1/120
720P 60P, Marvels 3.3, 1/250
720P 60P, Marvels 3.3, 1/500
720P 60P, Marvels 3.3, 1/1000

These are the shots I'm going to attempt to give me a chance to mix and match. I'm having a hard time believing anyone right now. The math isn't adding up for me.

I do have another question. Is the aperture setting going to influence the Motion Blur? I plan on sticking to F4 while shooting the action.
Click to expand...

You are thinking way to deep into this. Just know that the higher shutter speed you use will translate to a smoother slow motion. 120 will look better than 60
 
Thanks Rick, I see we're on the same page. The problem I'm having is that I'm going to ramp the slo mo and I've got no experience matching cameras or doing slomo so I'm trying to figure it out in my head before I test. Thanks everyone who have contributed so far.
 
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