Question about doing fast motion effects.

[Ryan Elder]

For a project, I want make a car look like it's going faster than it is, and I thought I would speed it up somewhat in post, and add motion blur.

I researched more on doing this and some sources say to shoot at a high frame rate, like 60 fps or more, because that will make the fast motion look smoother. Where as others say to shoot in regular 24 fps and just take out what frames you need to in post.

However, if 60 fps would look smoother, and I wanted to cut it down to 18 fps in post, would 60 fps really make a difference in smoothness if 42 frames per second are taken out?

It doesn't look like there is much difference to me whether it was originally shot in 24 fps or 60, if all there is, is 18 fps in the end. Unless I am wrong?

[Brian Drysdale]

I've never tried shooting at 60 fps for this making cars go faster, although I've shot at a slower frame rate, the latter being the standard method in westerns for horses.

The downside is that if you want a car to look like it's going fast, you need to drive a car fast, because the dynamics change with speed. That's why they close off road for filming this stuff, for you budget level I wouldn't put too much weight on high speed car shots for dramatic effect unless you've got a stunt driver(s) and access to closed/private roads.

For really scary stuff nothing beats the Class B rally cars

Rally Group B - Tribute - YouTube

As an aside, in the days of the 55 MPH speed in the US, it was amusing to see a shot of the speedo reading 70 MPH to indicate speed. That was the speed limit in the UK at the time, so wasn't that impressive.

[Ryan Elder]

Oh okay, but is possible to lower the frame rate to make a car look like it's going faster though? I was watching the making of The French Connection and they talked about how the car chase shots are at 18 fps, to make the car look like it's going faster. So could I therefore, cut it down to 18 fps successfully?

[Brian Drysdale]

Yes, but the car in the French Connection (I assume in the subway train chase) was already going fast. It just sharpens things up a bit, I've shot 18fps at normal car speeds and you wouldn't notice much difference.

The French Connection (4/5) Movie CLIP - Chasing the Train (1971) HD - YouTube

Given our urban speed limit of 30mph. a car would appear to be going 7.5mph faster. It's not high speed chase stuff and quite a few cars do 33 to 35mph normally, so you do need more speed and use maneuvers that give the impression of speed.

[Ryan Elder]

Oh okay sure, thanks. But I thought I would still take out some frames to sharpen it up a bit if that helps. When you say you shot 18 fps, does that mean you had access to a digital camera than can shoot at 18 fps?

I cannot find a camera that goes under 23.976 fps. I tried some tests on mine with magic lantern, and took it down to 6 fps, but it stops recording after a couple of seconds. But would anything under 18 fps be too much fast motion?

[Brian Drysdale]

This was using a film camera.

[Ryan Elder]

Oh okay. Well one person I asked said that when you speed up objects, you should shoot at a high frame rate like 120 fps he says, cause that makes speeding up to fast motion look smoother. But if you are going to cut it down to 18 frames, does it really make a difference shooting in 120 fps, if all you have is 18 fps left in edit?

[Brian Drysdale]

You won't have as much image blur if you shoot at 120 fps because of the faster shutter speed (you"ll need to ass it in post). It sounds like someone is puling your leg. It'll only be smoother if you are plat back in slow motion. it's the reason why 32fps or 36fps are used, because of the very slight slow motion that smooths things out when okayed at the standard 24dos,

Not although you'll be using it, but I gather the Arri Alexa can shoot at lower frame rates,

[Ryan Elder]

Yeah okay, I think the vfx person I talked to was confused and was applying the high framerate method when it comes to fast motion, when he was probably thinking slow motion. Or maybe he thought it would be good for both.

So if I want fast motion then in post, there is no reason to shoot over 23.976 fps then?

[Brian Drysdale]

No, shooting at your standard frame rate will be fine.

[Ryan Elder]

Okay. Well I took a test shot of some motorcycles and speeded it up in post, with different settings, but which one looks more convincing?

motorcycle speed test 4 - YouTube

motorcycle speed test 3 - YouTube

[Brian Drysdale]

It's be the speeded background action that gives it away. You need to test the same action as in your film, if your shots just consist of motor bikes zipping through the frame, that fine but it it doesn't prove your action for say cars driving towards you or going around a corner.

[Paul R Johnson]

I thought they both look 'messed with'.

YouTube (Short URL)

This looks like he's riding really fast, but I suspect it's not, and the sound of the bike high revving completes the illusion. Naked skin flesh, as in without helmet ripples above 40mph, as any biker knows too well. In the final shot, the low angle makes it look faster - I bet the scene didn't break wind!

[Ryan Elder]

Oh okay. well what about The French Connection car chase for example where they undercrank to 18 fps... How do they make it look good and not make it looked 'messed with'?

[Brian Drysdale]

In The French Connection they are already driving fast. To them, the thing to beat was the car chase in Bullet

Are you going to be able to drive the vehicles faster than the urban speed limit?