Shutter Speed @ high fps

[Tehben Dean]

If shooting for example at 48fps with a 24fps timebase is there a reason to have the shutter speed at 1/96 vs leaving it at 1/48? Which one will give "normal" motion blur?

Is there more to the 180º rule then mechanical shutter restrictions...?

 

[Keith_D]

At 48fps, 1/96 shutter =180 degree (Often refer to as "normal" blur motion.) 48fps, 1/48 shutter = 375.7 degree (more motion blur.)

 

[Tehben Dean]

Yes, but shouldn't it have the same motion blur as shooting 24fps @ 1/48 shutter.?

If you are shooting at 48fps, 60fps or 120fps surely it will look closer to 24fps motion blur if you shoot as slow shutter speed as possible rather then shooting a 180º shutter....?

 

[Doug Beatty]

I understand your thinking that since the frames advance faster in 48fps it would mean each frame would advance twice as fast and be exposed to light for half the amount of time it normally would at 24fps, negating any additional motion blur.

I think the trick of it is if you were to conform 48fps to a 24p timeline, you would essentially be going back to 180 shutter, but if you kept your timeline at 48fps, it would be 360 and blurry.

Of course this is a total shot in the dark, though. I'd be interested to see some tests.

 

[D Fuller]

The reason for using the 180 degree shutter is that the normal way we look at motion is with the 1/2 dark, 1/2 picture cadence of 24 fps/180 degree shutter. Even iff you speed it all up on exposure, you're still viewing it at the 24 fps rate, so a 300 degree shutter will not have the "normal" cadence, and won't look the same.

BUT... slomo is an effect, so the "normal" cadence may have no value at all to the shot. I shot some white-water rafting, over ranked, but with a very short shutter speed, because I liked the sparkle the short exposure gave to the water. Testing is good. And pre-thinking the shot is good too. You really need to be able to play the shot in your head and imagine the final result.

 

[Tehben Dean]

Thanks for the response David.

So even though 1/48th shutter at 48fps will have the same motion blur as at 24fps our eyes are not used to seeing a stream of images which is a constant recording without any on/off or missing time between frames because the shutter is affectively always open? This will maybe make the footage seem to smooth?

I was shooting some stuff at 60fps and told the guys I was working with that since there was no mechanical shutter I saw no reason to shoot at 1/120 shutter when the camera is capable of shooting at 1/60.... but it got me wondering.

I will definitely have to play with this and see how the difference looks and feels on screen.

 

[Domenic Barbero]

ive done tests with the 7d. 1/120th shutter @60fps definitely looks better than not changing it. I messed up on one shoot and shot 60 @60 and was very disappointed with my slow mo results. Also you have to factor that in for light loss everytime you wanna do slow mo.

 

[Stephen Aldridge]

I've shot and edited a lot of sports action and I've shot hours and hours of footage at 60 fps and I'm always grateful for my still photography experience because I know that when I'm shooting sports action, if I was shooting stills, a 1/60 second shutter wouldn't be near fast enough to get a really nice sharp picture. A 1/120 second shutter is much sharper and clearer and since you're going to be watching it in slow motion it gives you more time to look at the individual details and with a 1/60 second exposure, any fast motion gets blurry in a hurry. Sometimes, you might need that extra light to get a good exposure but I would rather turn up the iso, or get more light on the subject than lower my shutter speed.

 

[Julio Quintana]

For "normal" motion blur at high frame rates, always set your shutter to "Relative" and not "Fixed". Relative ensures that the shutter speed is always the same "angle". For example, 180 degrees at 24fps is 1/48, but 180 degrees at 48fps is 1/96. Relatve mode automatically adjusts the shutter speed to ensure consistent motion blur across different frame rates.

 

[Kwan Khan]

Agreed with Julio

 

[Tehben Dean]

I guess I'm still seeing it as "actual" motion blur stays consistent across "actual" shutter speed. So why does "perceived" motion blur stays consistent across frame rates with a 180º shutter? I guess this is because in general we shoot fast moving objects at high frame rates to slow them down and in order for them to have the same motion blur look as "normal" speed 24fps 1/48 we have to have a higher shutter speed to compensate.

If this is the case then for more scientific results the shutter speed should theoretically be based on how fast the object you are shooting is moving vs how many fps you are at.

Thanks for the clarification guys, making more sense now

 

[Mitch Gross]

Think of it as not relative to the shooting speed but to the playback speed. Conventional motion blur (ie, what we're all used to seeing) is a time reference from half the actual time gap represented. Meaning that images viewed 24 times per second are gathered of time from 1/48th of a second, and our brains are taxed at a consistant rate in order to have persistance of vision fill out the other half of the event arc. When the relationship of half exposure time to event time is changed, our perception of it does as well. This remains true even at high frame rates, so the 180 degree rule still holds, in general.

That said, there are plenty of situations where altering that exposure window can go completely unnoticed and plenty of other times when it can be a useful effect. Remember that it is all artifice in some form or another, but there are conventions that we are used to seeing. The world of extreme high speed (frame rates beyond what the RED cameras are capable), I find that I can open up my shutter angle to a virtual 360 degrees and can rarely perceive a difference. But that is part of the emotional contextual artifact of extreme slow motion playback. 1/1000th of a second v. 1/2000th of a second becomes a very different issue to 1/48 v. 1/96th.

 

[Harry Clark]

As usual, Mitch sums it up nicely. And up so early after the big presentation at Abel yesterday!
Julio is right too.
And in my opinion, the labels "Relative" and "Normal" in the Red scheme of things is confusing. In any customary world of filmmaking (whether film or digital) "Normal" would make the shutter behave as expected (1/14th at 24, 1/96th at 48, assuming a 180 degree shutter angle) The fact that you have to go out of your way from the camera default, set it to "Relative" (whatever the hell that means) and stare at a yellow setting (which implies you have set it to something unusual) is bizarre.
And to veer off-topic further, can we have the camera display (whether Epic, Scarlet, or Red One) show 23.98 when we are shooting 23.98? The fact that the display says 24, but means 23.98, is GUI programming laziness, or something. Oy. If I set the camera to 23.98, I want the large type on the display that everyone can see to read 23.98. I don't want to have to double check that I'm not in Varispeed, shooting 24 on a 23.98 project. I REALLY would have expected this quirk to be fixed in Epic but it's still the norm.
Cheers,
Harry

 

[Tehben Dean]

Thanks David, Julio, Mitch for the detailed explanations!

 

[Rob Parkin]

Surely 1/48th shutter speed is to help blend the huge gaps between frames when shooting 24FPS, this reduces stuttering in any motion in the shot. If you're overcranking then that gap between frames is vastly reduced meaning smooth motion. The last thing you want to do to crisp slow motion shots is ruin them by blurring all the detail using a 360 degree shutter. There's no point trying to think of it in relation to what we see because we can't see in slow motion, therefore all the rules change. If you're shooting slow motion use the shortest shutter speed you can to preserve as much detail and smoothness in the shot.
This is why in my opinion phantom shots look so good because even cinematographers obsessed with motion blur are forced to at least match the shutter speed to the FPS, which at 1000FPS leads to a nice short shutter and beautiful slow motion.

 

[Mitch Gross]

This is true to some extent but certainly not a hard & fast rule as you imply. For instance, if you want a water pour to have a smooth, flowing quality then a longer shutter with greater motion blur is preferable. But if you want a crisp, poppy feel to the water droplets, perhaps for a soda spot, then a very narrow shutter is desirable.