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class="style17"> Shutter Angle Combined With FPS

>Published : 8th October 2008

>Hello All,

>I am about to shoot a pop promo and I would like to explore shooting at different shutter angles on a hi-speed SR3. I have not have any experience of this although I am aware how to set the angle and make exposure compensations.

>However, could anyone explain the different looks achieved through this change in shutter angle. I believe it produces strobing effect most notably seen in 'Saving Private Ryan' and also that it creates a harder look to the image. Could anyone elaborate?

>Also what happens if this is combined with a change in frame rate? Would shooting at 50fps at a 90 degree shutter cancel each other out?

>I would like to experiment with shooting at say a 45 degree shutter angle and 6 frames per second and then transferring in TK at 6fps. Or 100fps and transferring at 100fps. What effect would this create? Is there a reference for these questions? Anything on the net?

>Many thanks in advance

>Lol Crawley
UK


>Lol Crawley wrote :

class="style18">>>Also what happens if this is combined with a change in frame rate?
>>Would shooting at 50fps at a 90 degree shutter cancel each other out?

>The frame rates you quote don't cancel each other like an inverse relationship, but you might need to go to 45 degrees to notice any difference at all compared to 50fps at 180.

>Unless the motion you are shooting is extremely fast, like a tight shot of sprinting horse hoofs, you start to lose the effect of the 45 degree shutter as you overcrank to 50-60fps since the increase in "temporal sampling" and the 50 fps shutter speed is outweighing the narrow shutter angle itself. Objects need to displace themselves quickly across the screen for the shutter effect to strobe. If its moving slowly across the screen when you're viewing it in dailies, then its not as choppy, if that's what you're looking for.

>As for xfer speeds, I've toyed with xferring as high as 60 fps. It looks sort of like having shot 30fps xferred at 30fps with 90 degree shutter. Some have shot 50fps for PAL, or 60fps for NTSC, so that each frame is transferred to a separate field, in hopes of solving a moire issue. But I would think this is rarely required. Above those respective frame rates (with equal transfer rates) you're not really gaining much, other than burning a lot of film for a higher shutter speed.

>I wish the SR3 went down to a 15 or 22.5 degree shutter, since that's where it gets really interesting.

>For the slower speeds, also, try 8 or 10 fps, xferred at 8 or 10 fps, with 45 degree shutter.

Mark Doering-Powell
LA based DP


>Lol Crawley wrote :

class="style18">>>...as frame rate increases, the intended 'strobing' effect of 90 degree shutter is reduced. An even >>smaller shutter angle... is needed to maintain this strobing effect at a faster frame rate. Correct?

>That's correct.

class="style18">>>I wish the SR3 went down to a 15 or 22.5 degree shutter, since that's where it gets really >>interesting.

>You get crisper images (less motion blur) at 15 to 30 degrees which takes care of most needs to get some chatter into the image. 45 degree is ok, but its often on the cusp at lower frame rates. The lower your fps, the narrower a shutter angle you also need for strobe since now you're also slowing down the shutter via frame rate. But you knew that.

>In essence, the further your fps from the normal 24-30 fps range, the narrower a shutter angle you need to get some strobe.

As for your other questions... shooting 15 fps and xferring 6 fps, or what have you. there are a gazillion ways you can do this. that's the beauty of it. It all depends on the motion of the subject, the panning speed and FoV, and what you're after. You really have to shoot some tests and see what you like.


Mark Doering-Powell
LA based DP


class="style18">>>"And, the fx house was very freaked about possible image blur thus creating matte tears...so I >>suggested shooting and transferring at 60fps...which we did. Talk about a very clean image! The >>mattes worked great and the image looked like hyper video."

>Nowadays it's pretty easy to put motion blur back in with software after matting; RevisionFX Reelsmart Motion Blur, available for everything from inferno to After Effects, being the most used. It uses "optical flow", which tracks picture elements through the scene.

>Tim Sassoon
SFD vfx & creative post
Santa Monica, CA


>Lol Crawley wrote:

class="style18">>>would like to experiment with shooting at say a 45 degree shutter angle and 6 frames per second >>and then transferring in TK at 6fps.

>Depends on action in the frame and how much temporal displacement the subject makes between samples. Skinny shutter on a talking head @ 24 doesn't look like much, skinny shutter on some one serving a tennis ball @ 24 looks very stroby and there is quite a bit of displacement between frames.

>You really have to tune frame rate and shutter to what is in front of the camera.

>Mark Smith
DP NYC