Shutter Speeds

[Chris Walters]

I was wondering if there are any typical shutter speeds that give you certain results. Like how f-stops give you a mathmatical amount light reaching the film plane. Obviously 180 is the normal, but are their any typical shutter speeds the most people shoot to get a certain effect like the over used example of Saving Private Ryan.

 

Also in terms of fps I understand the slo-motion and sped up trick of alter the fps, but are there standard fps to get a desired effect or does it all depend on the speed of the action. I understand that if you want something to go half as fast you shoot at 48 fps and obvious twice as fast at 12, but are there a general numbers DPs use or is it something they just test for. Thank you very much for pointing me in the right direction.

 

Chris

[Jonathan Bowerbank]

For shooting TV's, people adjust their shutter angle to 144 to sync up with the TV's scan. A 90 degree shutter angle will get you that Private Ryan or Gladiator effect by eliminating the motion blur from the action.

 

I know a few DP's out there when going for slow motion like to shoot even higher frame rates than 48, so if it turns out to be too slow, they can always speed it up a bit more in post if perhaps 48 turned out to be good enough.

 

I don't see too many people shooting under 24 fps unless it's for some weird old timey effect. For your own experience though, you might wanna consider shooting a roll at various frame rates to see the effects. For instance, you'll notice the motion blur that occurs when shooting 12 fps, requiring you to close down the shutter in accordance.

[Chris Walters]

I was wondering if there are any typical shutter speeds that give you certain results. Like how f-stops give you a mathmatical amount light reaching the film plane. Obviously 180 is the normal, but are their any typical shutter speeds the most people shoot to get a certain effect like the over used example of Saving Private Ryan.

 

Also in terms of fps I understand the slo-motion and sped up trick of alter the fps, but are there standard fps to get a desired effect or does it all depend on the speed of the action. I understand that if you want something to go half as fast you shoot at 48 fps and obvious twice as fast at 12, but are there a general numbers DPs use or is it something they just test for. Thank you very much for pointing me in the right direction.

 

Chris

 

To add to my last question, when changing the fps mid shot do you change the fstop to compensate for the increase or decrease in exposure? I think this is whats called ramping. Is this done by hand or is there a device that compensates when you change the speed. Or can the shutter speed that is sometimes changed? OR is all this done in post?

[Chris Walters]

For shooting TV's, people adjust their shutter angle to 144 to sync up with the TV's scan. A 90 degree shutter angle will get you that Private Ryan or Gladiator effect by eliminating the motion blur from the action.

 

I know a few DP's out there when going for slow motion like to shoot even higher frame rates than 48, so if it turns out to be too slow, they can always speed it up a bit more in post if perhaps 48 turned out to be good enough.

 

I don't see too many people shooting under 24 fps unless it's for some weird old timey effect. For your own experience though, you might wanna consider shooting a roll at various frame rates to see the effects. For instance, you'll notice the motion blur that occurs when shooting 12 fps, requiring you to close down the shutter in accordance.

 

Thank you so much... do you know the corrilation between the fps and the shutter... if its 12fps would you double the shutter speed to elimnate the motion blur?

[Jimmy Browning]

There's also an interesting trick I heard of but haven't tried yet. Undercranking and having the talent move twice as slow, or overcranking and having the talent move twice as fast. The net result is that the talent should be moving at a normal speed in the final footage, but because they're human and can't exactly replicate twice as fast and twice as slow, the movement takes on a surreal quality. It seems to be normal speed but not quite normal looking.

 

I just 1st AC'ed on a project that had done some tests with this but I haven't seen the results yet.

 

Jimmy

[Jonathan Bowerbank]

Thank you so much... do you know the corrilation between the fps and the shutter... if its 12fps would you double the shutter speed to elimnate the motion blur?

 

In this instance it would be referred to as shutter angle, rather than shutter speed. But yes, you would actually 1/2 the shutter speed from 180 to 90 if you're shooting at 12 fps and want to eliminate the excessive motion blur.

 

To go back to the "shutter speed" issue, it can be expressed in shutter speeds, but it makes it easier to say shutter angle since you're working with a shutter adjustment that works with angle of the shutter's opening. But, in the language of shutter speed, at 24 fps with a 180 shutter angle, you're effectively shooting at a 1/48 shutter speed, and at a 90 degree shutter angle you're shooting at a 1/96 shutter speed. At 12 fps with a 180 shutter angle you're at 1/24 shutter speed, which will explain the blurring.

 

If you want a somewhat cheaper way of testing things out, you can get an SLR camera and just try shooting some action stills at various shutter speeds, 30, 60, 125, 250, etc...

[Ralph Keyser]

To add to my last question, when changing the fps mid shot do you change the fstop to compensate for the increase or decrease in exposure? I think this is whats called ramping. Is this done by hand or is there a device that compensates when you change the speed. Or can the shutter speed that is sometimes changed? OR is all this done in post?

 

Some camera systems do allow this, and I've seen this type of control from Arri. They need an electronically controllable shutter and frame rate, and I've always seen an external box that handles this function. It's usually an extra bit of kit that they only rent for the days the effect is needed. On the control box, you select the starting frame rate and shutter, the finish point, and the rate of change. Then it's just a matter of pushing the go button at the right point. Some of the boxes will permit you to program two or three of these ramps to use in sequence.

[Jonathan Bowerbank]

Some camera systems do allow this, and I've seen this type of control from Arri. They need an electronically controllable shutter and frame rate, and I've always seen an external box that handles this function. It's usually an extra bit of kit that they only rent for the days the effect is needed. On the control box, you select the starting frame rate and shutter, the finish point, and the rate of change. Then it's just a matter of pushing the go button at the right point. Some of the boxes will permit you to program two or three of these ramps to use in sequence.

 

It'd probably be more cost effective to just go ahead and shoot the entire thing at high speed then ramp down in post, wouldn't ya think? The risk and margin of error is so tight with that kind of rig, not to mention the rental price and time spent on just prepping it would add more cost than just shooting the little bit of extra film.

Edited August 12, 2007 by Jonathan Bowerbank

[Michael Nash]

It'd probably be more cost effective to just go ahead and shoot the entire thing at high speed then ramp down in post, wouldn't ya think? The risk and margin of error is so tight with that kind of rig, not to mention the rental price and time spent on just prepping it would add more cost than just shooting the little bit of extra film.

 

I've ramped in camera many times (always Arri), and the exposure compensation is flawless. Never a problem. There are two ways to keep constant exposure: with an external iris control unit or with an internal electronically-controlled shutter. Both work great. With an iris pull you get a depth-of-field change during the ramp; with a shutter change you get a motion-strobing change (the shutter angle has to be 180 for the fastest frame rate programmed). Panavision also has a "smart shutter" feature on some of their cameras for ramping.

 

Shooting everything high-speed also renders each frame with very little motion blur, so that has to be added in post if you want motion to look normal at 24fps.

 

As for "standard" shutter angles, there's 180, 172.8 for synching to 50Hz. sources at 24fps, 144 for synching to 60Hz. sources at 24fps, 90 and 45. 90 and 45 degree shutter angles are useful because they reduce light in full f-stops, so exposure compensation is easy to calculate.

 

For frame rates, popular ones include the "HMI-safe" rates of 24, 30, 40, 60, and 120, which synch to the pulsing of HMI lighting without flicker. Almost any other frame is possible with variable speed cameras (within the limit of the camera; many synch-sound cameras only go up to 50fps), so the choice of alternate frame rates is pretty much a judgement call. Different DP's have their favorites, and the effect of an off-speed frame rate is relative to the speed of the motion being photographed.