Shooting slow-mo with lip sync

Oktay Ortabasi · March 22, 2005

First of all excuse my ignorance on this subject. Here is my situation:

Shooting on 35mm, probably 12mm prime. 60sec song in one take with a steadicam, moving through a party. Singer is walking forward looking into lens.

OK director wants him to sing to a track that is speed up by 25% and the shoot slow mo to have him sing on tape at normal speed but his body will move at a slower pace.

First question: I should shoot at 30fps which is 25% faster then 24fps (If I telecine at 24fps) right?

Second question: Will this give just a slight slow-mo look. Enough to notice and give it a "cool vibe?"

Third question: I also wanted to use a 45 or 90 degree shutter to give it that sharp but strobbed look. Which one is going to yield that typical "music video look." That's a sort of lame question but basicly how different do these two shutters look.

Forth question: So now I am shooting at 30fps and lets say a 90 degree shutter. Will I have flicker issues with lights on non flicker free balasts. I am shooting in the US so 60Hz is my AC frequency. As far as I understand 30fps is a flicker safe frame rate at any shutter angle right? It devides into 60Hz perfectly. Is there a formula for calculating flicker free frame rates? What property does the outcome of the formula have to have to be flicker free?

Fifth question: If the director wants to do in camera speed changes, then I will be crossing through all kind of flick and non flicker frame rates right? So I'll have to make sure all light sources are flicker free right?

Sixth question: What 35mm camera could handle doing 30fps and a 90 degree shutter? What camera could do that and in-camera ramping and aperture pulls? All of this with a remote of course because we are on a steadicam.

Thanks to anyone who take the time to answer my questions.

Michael Nash · March 22, 2005

It's late and I'm whooped after a 12 hr exterior shoot day (two crane builds and tear-downs), so I'll try to answer your questions as well as my brain will allow at the moment.

>First question: I should shoot at 30fps which is 25% faster then 24fps (If I telecine at 24fps) right?

>Second question: Will this give just a slight slow-mo look. Enough to notice and give it a "cool vibe?"

30 fps is slow enough to be noticeable when transferred at 24 fps. Even 26 fps appears slower than normal. The frame rate you choose is determined by the action and the look you want, and I can't answer that for you. It's something you'll have to test for yourself. 30 fps is 25% faster than 24 fps.

>Third question: I also wanted to use a 45 or 90 degree shutter to give it that sharp but strobbed look. Which one is going to yield that typical "music video look." That's a sort of lame question but basicly how different do these two shutters look.

That "sharp but strobed" look kind of runs counter to the "smooth and languid" look you get by overcranking. Technically you can do both, but it's kind of like taking one step forward, one step back. That stroby motion you get with a narrow shutter makes action look like it's faster than it really is. Again, you'll have to test the results you see from the two shutter angles. Keep in mind that a 45 degree shutter requires two more stops of light, on top of the 1/4 stop extra needed for 30 fps.

>Forth question: So now I am shooting at 30fps and lets say a 90 degree shutter. Will I have flicker issues with lights on non flicker free balasts. I am shooting in the US so 60Hz is my AC frequency. As far as I understand 30fps is a flicker safe frame rate at any shutter angle right? It devides into 60Hz perfectly. Is there a formula for calculating flicker free frame rates? What property does the outcome of the formula have to have to be flicker free?

30 fps is HMI safe at any shutterangle. The formula is known as "twice the frequency rule," meaning any frame rate that divides evenly into twice the power frequency is safe. 30 fps divides evenly into 120. 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 30, 40, 60, 120 fps.

>Fifth question: If the director wants to do in camera speed changes, then I will be crossing through all kind of flick and non flicker frame rates right? So I'll have to make sure all light sources are flicker free right?

Right.

>Sixth question: What 35mm camera could handle doing 30fps and a 90 degree shutter? What camera could do that and in-camera ramping and aperture pulls? All of this with a remote of course because we are on a steadicam.

Workhorse camera for this type of thing: Arri 435. There are other cameras you could configure to do this with enough accessories, but that's not really steadicam-friendly. The 435 is a proven machine for this. Last time I did it there was still a cable from the RCU to trigger the ramp, and you needed two assistants to share focus pulling and ramping duties in steadicam mode.

John Mastrogiacomo · March 22, 2005

30 fps is HMI safe at any shutterangle. The formula is known as "twice the frequency rule," meaning any frame rate that divides evenly into twice the power frequency is safe. 30 fps divides evenly into 120. 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 30, 40, 60, 120 fps.

Does this rule also hold true for Kino-flows? :huh:

Rolfe Klement · March 22, 2005

Kino lights with a Kino power supply are flicker free - but if you go over 10000 fps you might have issues :)

thanks

Rolfe

Adam Frisch FSF · March 22, 2005

Out of hard experience I just wan't to raise a flag for the whole percentage thing. It gets confusing very quickly since the camera speeds up but the track slows down and percentages

can be different depending on from which end you calculate (at least when you have limited mathematic skills like I do). A 25% add on to a sum is easy enough, lets say 100 for convenience = 100x1,25=125. But if you already have the 125 and want to count backwards, then 125x0.8=100 as it turns out which would indicate a 20% decrease. :blink:

Oktay Ortabasi · March 23, 2005

Thanks for all the info everyone. Sorry for the basic questions but just wanted to get things right. I talked to the director today and we are going to take the 45 degree shutter out of the set up. What M.Nash said about the slow-mo and the 45 degree shutter pulling the look in two different ways makes a perfect sense. Thanks. As far as the percentage thing I look at it this way: I am speeding up the camera by 25% form 24fps to 30 fps and the sound is being speed up 25%. Then in post I am playing the image at 24fps and bringing the sound back to normal speed. The media, sound and audio, are going through the same process. Of course we'll still have to slow the sound down a touch to match the 29.97 frame rate of video. I guess I could shoot based on 29.97fps then for the slow mo shoot 37.46fps. Transfer at 29.97 and just transfer the sound straight. But I always feel that shooting at 29.97 kind of gives film a little video look to it when transfered.

Thanks again for all the responses.

Elhanan Matos · March 24, 2005

Kino lights with a Kino power supply are flicker free - but if you go over 10000 fps you might have issues :)

thanks

Rolfe

<{POST_SNAPBACK}>

Ive noticed Kino Flows start flickering at somewhere around 200fps, these were Image 80's. I don't know if they flicker at frame rates lower than this, 200 was the slowest we shot that day.