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Shutter Angle & White

Published : 8th January 2007

Greetings,

I am shooting a high-energy montage of women models dancing against a white background using an ARRI 435. We will be zooming in and out and plying with the 435s capabilities. Something no one has done before I am sure.

1/. Using seamless White paper , how far over exposed should the background Spot Meter for white with minimal grain ? ( 5217 - Spirit HD Transfer to D5).

2/. Is 45degree shutter angle 'standard' to achieve that crisp flickering motion? What is the compensation for each 45 degrees?

3/. Silly question... Is there any visible effect when shooting with a 'radical' shutter angle while over-cranking 48 to 60 fps?

Thank you for any advice on Shutter Angle, Ramping etc..

To me the basis of these questions is so 'basic' I thought it best to post it here in Basic Cinematography.. humbled.

Sincerely,

David Rakoczy


>>2/. Is 45degree shutter angle 'standard' to achieve that crisp flickering >>motion? What is the compensation for each 45 degrees?

Even 45 degrees is probably too much - go for 22.5 or even 11 degrees.
Every time you cut the shutter angle by half, you open one stop. If 180 degrees is normal exposure, 90 degrees is one stop open, 45 degrees is 2 stops open, 22.5 degrees is 3 stops open, 11 degrees is 4 stops open (from normal)

>>3/. Silly question...Is there any visible effect when shooting with a >>'radical' shutter angle while over-cranking 48 to 60 fps?

More strobing, decreased exposure.


Both decreasing the shutter angle and overcranking have the effect of decreasing the exposure time for each individual frame, or "shutter speed" to put it into still photo terms. A faster shutter speed tends to "freeze" the action in each frame, making each frame appear "sharper" because there is less shutter blur.

24 fps = 1/48 second shutter speed, 48 fps = 1/96 second shutter speed, 96 fps - 1/192 second exposure time, etc.


Shutter blur is GOOD for movies because it helps make the 24 frame per second images flow together smoother. The brain smoothes out the action for us, filling in the information between frames.

To get that "Private Ryan" look, we would want shorter exposure times obtained by reducing shutter angle. The images look sharper and "jumpier" because the brain can't quite smooth out the action enough. If 24 fps is normal exposure, 48 fps opens one stop, 96 fps opens 2 stops.

Of course these are IN ADDITION to any compensation for smaller shutter angle (see above).

Doug Hart
1st Camera Assistant, NYC


Thanks Samuel.

That is exactly what Doug said "go 22.5 or even 11". Thank you also for the insight into using the shutter angle during a ramp to hold the stop instead of changing the aperture which will obviously alter the DOF.

Do you concur with Dan in regard to Spot Metering the White Background at 3 - 3 1/2 Stops over and no more for minimum grain perception?

'Smearing' I am not familiar with....??

David Rakoczy
DP/Dir


If you're talking about synced strobes a la Unilux the effective shutter angle (I don't recall exactly) is far far less than the 11.5 degree shutter angle & conventional light source. One cool thing you can do with those systems is to mix strobe & continuous light source so seems to me it might be better to use a normal shutter angle in these cases, then blend your frozen and your blur to taste.

-Sam Wells
film/.../nj


To clarify.. I will not be using Strobes (though that info is great to know for the next one). This show will be lit Tungsten with out the use of Strobes.

David Rakoczy
Dp/Dir


David Rakoczy wrote :

>>Do you concur with Dan in regard to Spot Metering the White >>Background at 3 - 3 1/2 Stops over and no more for minimum grain >>perception?

Hi,

I agree with 3 to 3 1/2 stops over with a spot meter on a white background.

Stephen Williams DoP
Zurich

www.stephenw.com


An of site post response.

Thanks Anthony!

You are the first to confirm the 45 degree setting. I have heard in the past that 45 degrees was the 'norm' for this effect but many have chimed in saying go 22.5 or 11.... obviously 45 is easier to light than 22.5 or 11.

Are there any others with an opinion to go 45 vs 22.5 and 11?

As far as the background goes I am going 3 stops over and yes I was concerned as well with the wrap around glow that could happen at a higher over exposure.

David Rakoczy
DP/Dir


If you look at the end of the first battle scene in 'saving' or at some of the performance shots in the recent my chemical romance vid (based on 'saving') you'll notice some shots have a vertical smearing of highlights caused by the rotating shutter being of sync with the film movement, so that the film is being transported while the shutter is open. The degree to which the phase is shifted is controlled by the shutter sync box, a Arri acc., and it can be controlled to extreme or subtle depending on your liking. It can be a good contrast to the hyper-crisp narrow shutter effect.

3 1/2 or 4 stops over key should give you a clean background.

And added bonus of phase shifting is the sound the 435 makes when you shift while running (especially at the more extreme end of the dial), it sounds like it's tearing itself apart, but that's normal. The first time you hear it it's a bit disconcerting though.

Enjoy and happy shooting,

Samuel Brownfield
DP/LA


David Rakoczy wrote :

>>You are the first to confirm the 45 degree setting. I have heard in the >>past that 45 degrees was the 'norm' for this effect but many have >>chimed in saying go 22.5 or 11...obviously 45 is easier to light than >>22.5 or 11.

Hi,

45 degrees is a good starting point, 22.5 degrees will be sharper. I think you need do a test and see which you prefer.

Stephen Williams DoP
Zurich

www.stephenw.com


David Rakoczy wrote:

> Are there any others with an opinion to go 45 vs 22.5 and 11?

Depends on how much camera movement, how kinetic the movement is in front of the camera, and the frame rate. If the subject is moving very fast and you are shooting 24fps @ 11deg shutter, there will be a good deal of subject displacement from frame to frame( and the subject will be crisp with little motion blur. An earlier poster suggested doing a pre viz with a video camera which is a fine idea. Get a DVX set it to 24 P try a shutter setting at 1/500, shoot your action, test it again at 1/1000 .

This test will give you a decent idea of what the image will look like at 24. As you film frame rate goes higher you have more samples per second and the crispness will still be there but the subject displacement from fame to frame will be smaller because of the higher sample rate, which smooths out the motion.

Mark Smith
I forget what I am today, probably mopper of floors
NYC


Hi David,

I agree with Mark that between 3-4 stops over your exposure will render a clean white. The question I have would be how well the white density\consistency will be maintained if you do any speed ramping... not sure if that's one of your intentions for the shoot.

If you ramp from one frame rate to another and do an iris or shutter compensation, will you notice a big fluctuation in the exposure of the whites, especially if they're prominent in the frame?

How precise is the exposure compensation throughout the ramp between the speed and the shutter angle or the iris change? Will it require any finesse in post?

45 degrees will definitely give you a lot of strobing, depending on how much movement there is in the frame. Static subjects don't strobe as much as fast-moving ones.

The "streaking" effect, which is where the shutter is phased out of sync with the pull-down of the film, is most effective when there are highlights in the frame, like practicals. This is because the film is exposed while it's both held static in the gate for a moment and
then when it's yanked downward as the frame advances, and the highlights expose faster than the blacks. I think it's used in the opening sequence of "The Mothman Prophecies", if I remember correctly. It's my understanding that not all 435's are set up for this, so you'd need to request it from the rental house.

Best Wishes,

Graham Futerfas
Los Angeles based DP
www.GFuterfas.com


Yep, you are correct Graham, when you prep you have to have them install the circuit for the phase shift. On the 435 the shutter will compensate perfectly for exposure, within the 4 stop range. If you ramp beyond that your whites, as well as the rest of your exposure, will vary.

Samuel 'loves a good ramp' Brownfield
DP/LA


David,

When I'm in your situation I use a Kodak Grey Card Plus which has samples of 3% (black) reflectance, 18% grey and 90% reflectance (white).

After lighting the white BG for evenness I then stand with the card next to the white cyc/BG/whatever and spotmeter the grey, the card's white area and the cyc's white. Then I know where each of the samples will end up being exposed depending on the stop I put on the lens. It also tells me how white my cyc really is compared to the card white.

Normally the difference between the 18% grey and the 90% white is approximately 2 1/2 stops. If I want the white cyc to be at 95-100 IRE white in TK I then put my lens stop between 2 and 3 1/2 stops below the cyc spot reading. Then I key the subject (the important part of the equation) in front of the cyc to that stop. Where in that 2 - 3 1/2 spread I choose to set my aperture depends on subject skin colour, reflectance and my own personal mixture of goat eyes and bat wings. And how much detail I want in the white of the cyc: way blown out dream sequence, infinity white verses "Hey there's a white wall in the background" white. Once I decide on a lens stop I can go back to using my incident meter until I do a final spotmeter check to make sure I didn't change the BG evenness in the process of lighting the foreground.

I find this approach works well for me on greenscreen shoots too. Only the ratios change.

This is my approach and of course, YMMV.

Let us know how it turns out.

Randy Miller, DP in LA


How much over-exposure you need for white whites is very much dependent on how you telecine.

With something like a music video the contrast is generally cranked way up and even 2.5 stops will give you burned out whites.

The white whites are a function of exposure and TK.

I would not push the white level too far as flare then becomes a serious problem.

If in doubt stick to 3 stops

--

Cheers

Geoff Boyle FBKS
Director of Photography
EU Based
www.cinematography.net


Read Ansell Adams 'The negative"

Dan Bronks
DP


Thank you ALL for your help! (ordered the book)

Re : smearing. My SR2 got out of phase/ sync once and I had a slight blurring on the left edge of frame (now repaired) so I imagine this is the same thing in a 'controlled' application. The smear is from right to left? Is it adjustable? Can you place a subject on the right side of frame and have highlights and hot spots on the left side of frame smeared? In other words can you creep the smear in at different increments so you could smear half the frame or just one third or just the edge?

I have used 535s and 435s a lot but all in narrative 'straight' cinematography situations and have never played with the bell and whistles. Believe me, this shoot is one huge test and we will put the 435 thru all its paces. I look forward to hearing it moan.

David Rakoczy


Hi David,

The smearing is up and down... the film is exposed while in motion, so if it's moving downward in the gate after being held still, then the highlights will be streaked downward in frame. If the film is moving into position, then the highlights will appear to be streaked upward (they're still technically streaked downward, but they are exposed from top to bottom). Remember that the top of the frame is at the physical bottom of the gate.

The effect is adjustable, even during the shot. You basically just dial in the amount of phasing you want. I suggest looking at examples of it so you know what to expect.

I'm not sure if you can choose the direction of the smear (up or down), meaning it's exposed while the frame is moved into position in the gate (pre-smear) or it's exposed while the frame is being moved downward out of the gate (post-smear). Kind of like a first curtain or second curtain flash sync with a still camera. Does anyone know if you can select the direction of the phasing so it could streak up, down, or both? I believe when I've seen the effect, it's both.

I'm also wondering if anyone has thought to turn the camera on its side to get left-right smearing. I saw that effect last night on a car commercial, where the brake-light smeared side to side as the car pulled out of frame, but I'm pretty sure it was done in post.

Graham Futerfas



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