Shutter Angles What They Do?

[Guest dpforum1968]

Hi All,

 

Perhaps some one can give me a brief course on how changing the shutter angle affects the image on film? I know that changing the angle affects the exposure time & image sharpness, but I've always shot with a 45 degree angle so I have nothing to compare the effects to.

 

What really changes using 180 degrees or 90 degrees? What are the benefits etc etc?

 

Thanks

DC

[Greg Gross]

Hello dpforum 1968,

Some cameras today you will find have a variable shutter(probably most today

do, you know Arri,Panavision). I've only had the pleasure of shooting some short

ends with these cameras. Lets say you have a camera with a 180 degree shutter,

if you set the camera angle to 90 degrees then you have 1/2 as much light for your

exposure. The shutter rotates. You can actually create a fade in,fade out by vary-

ing the shutter. I personally think thats a little amateurish though. You can create

strobic effects by varying the shutter, another method called skipping will make

something appear to be vibrating,all by varying the shutter angle. It takes a narr-

ow shutter angle to create a skipping effect. A change in camera speed will cause

a change in shutter speed. The shutter is basically a disk(which I think confuses

some people) with a cut out(opening) of 180 degrees. As the film moves into pos-

ition the disk covers the aperture,rotating some more the aperture allows the fra-

me to be exposed, it then covers it again for the pull down of an un-exposed frame. The shutter is rotating all the time, so the film is exposed 1/2 of the time

and covered 1/2 the time. With a camera speed of 24fps the film is exposed at

1/48 of a second(this is 1/2 of 1/24). If you know this then you can speed camera

up or slow camera down,adjust fstop for correct exposure . Maybe you are in low

light. Greg Gross,Professional Photographer

Student Cinematographer

[David Mullen ASC]

Are you sure you are shooting at 45 degrees? That's pretty bizarre. 180 degrees is the standard. At 24 fps, a 45 degree shutter angle gives you that jerky, choppy "Saving Private Ryan" / "Gladiator" motion strobe in action scenes. 90 degrees the same but it's more subtle than 45 degrees.

 

Shutter angle combined with frame rate determines shutter speed. Short shutter speeds gives you less motion blur. However, a certain amount of blur is necessary to create the illusion of smooth motion at 24 fps, since it is a relatively low frame rate and strobing is a real problem. Hence why stop-motion animation traditionally looked jerky because each frame was crisp with no motion blur.

[Andy O'Neil]

A possible benefit of changing shutter angle vs. aperture:

 

The iris diaphragm of the lens can be changed, but this would change the depth of field and may be more noticeable than shutting down a variable shutter.

[Guest dpforum1968]

Ah right, thanks David Mullen, I guess I am using 180 degrees. For some reason I thought 45. I've just been using the pre-set from the factory and you can't change it, I shoot 90% of my stuff at 24 fps. Ok must be 180 then, good to know.

 

Also you raise an interesting point about the "look" of the action scenes in Saving Private Ryan, using the 45 degree angle. I had always wondered how that was created, I thought it was a post effect. Thanks for that info, I'm actually working on a WWII piece in three weeks and there are battle scenes. Although we'd have to rent a higher end camera that we can change the shutter angle on, not sure if we have budget for that.

 

Thanks also to you other guys for your information.

 

I assume then most every film shoot is done at 180 degrees, so that it looks "normal". Unless one is going for an effect ie Saving Private Ryan.

 

Another question then: I notice some folks selling chroma key footage, ie people against green screen for use in keying. On the web site it says that all the shots are taken with the shutter angle at 45 or 90 degrees. So I assume there is some benefit to using 45 and 90 when working with green screen? It creates a sharper edge making the material easier to key????

 

Thanks again,

DC

[Guest Andy Sparaco]

Actually a variable shutter is very handy in the fact you get a faster effective shutter speed and consequently less motion blur. If you are shooting close-ups, water, liquids but don't have strobes or can't over crank the camera it delvers sharper results. The Eclair NPR,CM3 and Arri 2CV are the most common cameras with variable shutters. Some Arri-S's and also P+S retrofitted SR's have them.

 

Also if you need to knock down exposure 1 or two stops without changing f-stop, camera speed or filter. In very bright light you can reduce exposure without adding so much ND it is hard to see. Reducing a 50 ASA speed film to an effective 12.5 ASA with no change in viewfinder brightness on a sunny summer day in Miami is handy indeed.

[John Sprung]

I'm actually working on a WWII piece in three weeks and there are battle scenes..... 

So I assume there is some benefit to using 45 and 90 when working with green screen?  It creates a sharper edge making the material easier to key????

<{POST_SNAPBACK}>

Real WWII combat footage was shot with either B&H Eyemo's, which have a 165 degree shutter, or Arriflex model one's, which were pretty much the same as the 2A-B-C for shutter angle, IIRC, somewhere in the 170's. Going to a 45 or 90 degree shutter is something they decided to do as an effect on "Ryan", it's not historically justified. (BTW, if you ever find something that seems to be an Arri 2A, but the serial number is under 2000, it's a model one. They made about 1500 of them. No replacement parts are available because all the parts and equipment for making the model one were destroyed by the RAF and 8th Air Force.)

 

As for green screen, short shuttering would give you an unnaturally sharper matte line and insufficient motion blur. Motion blur is your friend. Without it, there is no illusion of motion, and no motion pictures. With zero motion blur, you have an excessively rapid slide show, not movies. Short shuttering to make the mattes sharper would really be throwing the baby out with the bath water.

 

 

 

-- J.S.

[Guest Daniel J. Ashley-Smith]

As for green screen, short shuttering would give you an unnaturally sharper matte line and insufficient motion blur. Motion blur is your friend. Without it, there is no illusion of motion, and no motion pictures. With zero motion blur, you have an excessivley rapid slide show, not movies. Short shuttering to make the mattes sharper would really be throwing the baby out with the bath water.

 

Trouble with that is that you need a fantastic keying system. Your typical system wouldn't remove the motion blur colour spills. Although if you have a good one, then it's ok.

 

Ultimatte do some unbelievable systems, pricey, though..

[Morgan Peline]

I watched 'Chung King Express' for the first time the other day. There was a lot of slow-motion blurry movement shots in the first part of the film.

 

Does this mean they shot 50fps of 75 fps but with a shutter angle of more than 180 degrees to get the blurriness?

 

Thanks

Morgan

[Guest Andy Sparaco]

You can shoot with increased sharpness and without stutter up to 90 degrees you start to push your luck at 75 degrees.

 

A 90 degree shutter improves sharpness in green screen work especially in 16mm/Super 16. Before the introduction of 7217/7212 you needed to push every angle possible to make it comparible to HD footage for composite.

 

No longer such an issue with the new Vision 2 stocks even 7218 does really well

[John Sprung]

You can shoot with increased sharpness and without stutter up to 90 degrees you start to push your luck at 75 degrees.

<{POST_SNAPBACK}>

It really depends on how fast things are moving in the frame, or how fast you're panning. Test it and you'll find that there are speeds that will skip at 90 but not at 180.

 

 

 

-- J.S.

[David Mullen ASC]

"Chungking Express" increased blur by shooting at very low frame rates (like 6 or 8 fps) so that the shutter speed with a 180 degree shutter was like 1/12th or 1/16th of a second. The footage had to be optically step-printed to repeat frames back up to 24 fps.

[Guest Andy Sparaco]

It really depends on how fast things are moving in the frame, or how fast you're panning.  Test it and you'll find that there are speeds that will skip at 90 but not at 180.   

-- J.S.

<{POST_SNAPBACK}>

 

Yes point well taken but at 24fps and with a 180 degree shutter you'll find that if you test there are speeds that will skip at 180 but not at 90.

 

In a lock down shot or a slow pan shot depending on the direction of the motion in the frame, the time of day,the relative motion of the moon and which way water swishes down the drain a 90 degree shutter will not stutter noticeably. :D

 

 

 

I constantly see "strobing" during panning shots today, which never would have been tolerated 15 years ago. What was considered a mistake then is a now a cutting edge technique. So as always "the eye of the beholder or check writer" is the what matters.

hmm... should I be a "sloppy' cinematographer or "old fashioned" today.

[Erkan Umut]

Yes point well taken but at 24fps and with a 180 degree shutter you'll find that if you test there are speeds that will skip at 180 but not at 90.

 

In a lock down shot or a slow pan shot depending on the direction of the motion in the frame, the time of day,the relative motion of the moon and which way water swishes down the drain a 90 degree shutter will not stutter noticeably. :D

 

 

 

I constantly see "strobing" during panning shots today, which never would have been tolerated 15 years ago. What was considered a mistake then is a now a cutting edge technique. So as always "the eye of the beholder or check writer" is the what matters.

hmm... should I be a "sloppy' cinematographer or "old fashioned" today.

 

Skipping (you say strobing) also related to the shutter position. If you expose the film by reflex mirror shutters at 45 degree position (not the opening angle!) btw the lens and aperture like in ARRIs, you gonna get more skipping while fast panning than the focal plane shutters like in Panaflexes or eclair ACL. Because the focal plane shutter is completely close to the aperture, so it means that it cuts the light at very narrow cone point (here we call the exposing light rays as a cone).

Also, contrarily panning to direction of shutter rotation causes more skipping.

[Chris Keth]

You sure dug up an old thread. ;)