[R Harkness]

In regards to the question of the thread title: as some have already indicated "judder" doesn't come only from the telecine process; it's also inherent in the limitations of 24ps film techniques and shows up on the movie screen as well. Since many here have been covering the telecine/video process-born version of judder, perhaps I'll blather a bit about the film-born version.

24fps is low horsepower - a very low "sample rate" - for capturing motion and that particular number-per-second makes for some odd artifacts. A classic is the "wagon wheel that starts going backward," - e.g. in westerns as a horse-drawn wagon with large wheels and long spokes begins to slow down, the spokes appear to briefly start going backward, and then reverse back to the proper direction. (It's not hard to figure out why that occurs if you think about it).

But the judder that is problematical to film cameras isn't actually a problem during fast motion or fast pans so much as "medium" paced (or medium slow) pans. A lot of effort goes into dealing with the limitations of 24fps in making movies. If you pan quickly all the film captures is blur, so a fast pan lasting too long will bug out your eyes like you can't focus. But it's ok as long as there is an object for your eyes to focus on in the frame, even if all the rest is a blur. So that's obviously why the actual relative movement of an actor or object within a frame tends to be restrained. In other words, the actor running through a crowd will generally be kept around one area of the frame so that at least he remains in focus even if everything else is blurred by the panning motion (likewise with space-ship flying scenes).

Judder becomes a problem especially with camera movement, e.g. a pan, that becomes medium tempo and is exacerbated by hard-edged, vertical objects - the nightmare scenario being the medium pan across a picket fence outside a house. If the pan is fast enough, the vertical boards of the picket fence will become blurred on each frame of film, creating a blurred-together look as we watch it on screen. This looks fairly natural to us, since objects in motion blur in our vision naturally (just wave your hand in front of your face, especially under low lighting if you haven't noticed it before). But if the pan gets slower, the individual pickets in the fence are captured with less blur, until you can see the more discrete, more defined pickets. But at 24 fps doesn't allow capture (at such a speed) of all the successive positions needed for a smooth motion. So
what you notice are the pickets stuttering across the screen, because the camera has only captured the pickets in position A...D...G...J...M.....instead of all the steps....ABCDEFGHIJKLM
(Or I....I....I....I....I....I instead of a continuos IIIIIIIIIIIIIIIII).

Something like this same phenomena is seen in movies like Private Ryan and Gladiator, which employed a technique sometimes referred to as "skinny shutter" (or 45 degree shutter), in which the shutter angle is changed such that
exposure time is reduced for each frame. So, just like raising the shutter speed on your still camera ensures a sharper image, you end up with sharper discrete images on each film frame. But you also therefore loose the "natural" looking blurring that is typically captured with motion on film. Hence when played back on-screen, the sharp images at 24fps allows our eyes to pick up the discrete
time sampling of the action, giving the image that sharp, but jerky look seen in the gladiator battles.

(And it's why stop-motion animation like Ray Harryhausen's work had that jerky quality. It wasn't so much due to a lack of ability on H's part - obviously he was amazing. But it was a limitation of the technique, because unlike regular real-time motion captured on film, which causes some blur, each frame of a Harryhausen's model's movement was a still motion, making for sharp images each frame and thus the stuttered movement like you see in gladiator. It wasn't until The Empire Strikes Back that this deficiency in stop motion animation was addressed and Phil Tippet created "go-motion," in which the models were actually moved a little with the shutters open, giving the image a natural bit of blur on each frame and restoring fluidity. For just these reasons artificial blur is added to motion in CGI characters/animation, to mimic the blur of "real" objects as captured on film).

But back to the picket fence....if the camera slows down still more, even though the individual pickets are caught with greater clarity, they will move more smoothly through the frame because, obviously, more frames-per-second were able to be devoted to the movement of each picket, making for smoother motion.

In fact if you read a cinematographer manual, such as American Cinematographer 35mm Manual, it has specific recommendations for panning speeds (also taking into account screen brightness, focal length etc), so as to avoid strobing and skipping effects.

This limitation is something that really bothered Douglas Trumbull (Special Effects supervisor for Close Encounters Of The Third Kind, special effects guy on 2001, director of Brainstorm etc). The low 24fps sample rate of film is such a limit on it's fidelity (speed any sampling system up - analog tape, digital what have you - and you increase fidelity), which is one reason why Trumbull created "Showscan," in which his company did many tests for arriving at frame rates that led to a clearer image and smoother motion. It's shot on either 65mm or 70mm film at 60fps with an extremely wide shutter angle of 180 degrees, making for a shutter time of 1/125 second. The very short exposure time makes for very sharp images, and the high 60fps sample rate makes for smooth motion. The combination makes for super-sharp images with natural motion. Too bad it didn't catch on
with the major film companies and was relegated to a theme-park "ride." But if you've ever seen it - wow! - you've never seen film look like that before. It's amazingly 3 dimensional-looking.

But, anyway, whenever I was shooting film I had to be conscious of judder scenarios and the general limitations of trying to capture motion at 24fps.
It still kind of drives me nuts when it occurs watching movies projected in theaters as well.

(Sorry for the length, but given this thread title I s'pose there must be someone interested in the details...and btw earlier there was a discussion wondering if the movement of film in the gates could be responsible for judder. However, each frame of film moving through a camera's gates is momentarily stopped for the film exposure. Obviously this is necessary, otherwise all film would be a blur. So judder and motion artifacts are a matter of exposure time and the low sampling rate of 24fps film).

Cheers,

Rich

(Been a long while since I've shot film at this point, so forgive if my memory is getting creaky).