Frame rates and shutter speed strategy

[Stewart Read]

Hi All

I am trying to understand better the effect of shutter speeds when shooting high frame rates in camera and then returning the footage to say 25fps in post production.

Could someone explain the math(s) and what strategy people are using to change the speed in post and retain acceptable motion blur for both the slomo and 25fps versions of the shot ?

Thanks in advance.

 

[Ksawery Jan Oroczko]

I thinks that is quite simple. Here is the short explaination: Set the timebase to 25 FPS. By using the 180° shutter rule: 75 FPS / 150, 90 FPS / 180, 120 FPS / 240 shutter speed you should be in 90% of all possible situations fine. In low light situations you might wanna break the rule, e.g 90 FPS / 120 shutter speed. The best is to experiment with the shutter to see the effect / Motion blur you get As a second step I would check out how the shutter reacts on 50/60Hz light sources. By using LED you should have no problem at all.

If you want to speed up slomo footage in post you might see some odd results (Especially with human movement) if you overcrank it. E.g you have your 120 FPS clips and make it faster, e.g. 25% (4x speed), than it should change in theory to 30 FPS, but the result might be that it doesn`t look good if its visible longer. Fast cuts might help.

 

[DC Chavez]

It all depends on the action happening in frame. As a general rule I shoot 24fps at 1/48th, 120fps at 1/250th and 240fps at 1/1200. I shoot a lot of cars and racing stuff, so getting detail in the wheels is important for me as the cars go by. I sometimes adjust the shutter speed if the cars are moving extremely fast.

 

[Ulf Krentz]

Stewart, if you speed up your slomo footage it will probably have that strobe-effect that is known from shooting at regular fps with short exposure times, no surprise and unfortunately no easy solution here. Depending on your subject you might shoot with a 360deg shutter and still need to add motion blur in post.

Cheers,

Ulf

 

[Stewart Read]

Thanks everyone. This topic came up after reading Christopher Probst's post about Eminen shoot.. still some more learning to do I think...

 

[Anton Shavlik]

Can't resolve add motion blur? Lots of compression algorithms track pixel movement, I feel like there's likely something similar that can add it back in if you're worried about shutter angle for one reason or another.