Movie Film Should Blur, Right?

A) I was wondering about movie film, and how we take it for granted. But, why does movie film work at all? Why doesn’t it simply see blurred images? Is the “frames per minute” the critical factor? (And, how many frames per minute is professional film, anyhow?)

B) Also, how is movie film developed? How can each frame receive the same chemical treatment for the prescribed length of time? I think I’ve seen pictures of a canister which holds a reel of film to be developed, but you’d think all the chemicals on the film would simply run… - Jinx

What you see on the screen is actually a bunch of still images flashed one after the other, with a black screen between images. So long as the frame rate is fast enough, your brain processes it as a continuous image. If the frame rate was too slow, it wouldn’t look blurred, but instead “jerky”.

Professional movie film runs at 24 frames per second. That’s fast enough for your eye to retain the image until the next one registers.

If I recall film developing units, the film basically is “dipped” into the solution and then run through a dryer. Back in my TV days, I recall our film editor complaining when a news crew got back so late that they had to pull the film out “wet” to get it on the air.

Standard cine film as in theaters is usually 24 frames per second. This is fast enough that the individual exposures don’t show motion blur most of the time but you certaianly can see motion blur in film. Lack of motion blur in action scenes is one of the things that made early CGI look fake.

Cine film is deveoped on a serpentine path that moves the film through each chemical tank so that any point on the film is in the solution as long as it should be. Think of the classic sea serpent with it’s body making a sine wave where each negative wave is in a different bathtub. The entire body of the serpent glides through developer, stop bath and fixer in the individual tubs.

I assume the OP is asking why the image on the screen isn’t one big vertical streaky blur as the film advances through the projector. IANAProjectionist, but isn’t there a shutter of some sort that blanks out the image while the projector advances to each new frame?

Presumably if the shutter is out of sync, that’s when you get the “top half of the image on the bottom, bottom half on the top” problem.

kunilou, that goes back a few days.

Everything’s shot in video now. :stuck_out_tongue:

Yes, and when the guy who runs the machine on odd days fails to renew the chemicals as scheduled, or the cogs in machine gets out of sync so it starts eating film, the “reporters” in the newsroom go postal.

Movie film is just as subject to blurring as still film. It’s most often seen when the camera operator pans too fast.

From here

To make it perfectly clear, the picture isn’t blurry because when the picture is taken, the film isn’t moving. The film moves in little jerks, stopping each frame in front of the shutter for a split second.

The film isn’t pulled through the camera or projector continuously, the movement is intermittent. It moves forward one frame, stops, then moves again.

In both the camera and projector there’s a shutter, but the shutters are different. In the camera, there’s a disk with a wedge cut out of it (how big this wedge is depends on the camera and in some cameras can be variable) that spins continuously. When the film is moving, the solid part is in front of the lens and blocks the light, so there is no motion blur (at least from the film moving, there can be motion blur if the object being filmed is moving too fast). When the film is stationary, the open part is in front of the lens, so the film is exposed.

There’s also another style of shutter, where instead of a spinning disk with a wedge taken out there’s a guillotine that drops and raises, but the purpose is the same.

There are shutters in all camera except those designed for very high-speed filming, where trying to move the film intermittently would just succeed in shredding it to bits. There, the film does move continuously and, instead of a shutter, there’s a rotating mirrored device that tracks the picture onto the film as it moves by.

In the projector, the shutter still has a solid portion that covers the film as it’s moving, so you don’t see a vertical blur (although you wouldn’t see much of one anyway, the intermittentness of the picture is enough to fool your brain, as is evident from many of the old shutterless toy projectors of the '20s), but it also has one to four additional solid segments that block the film even while it’s not moving. These are to minimize the flicker that would otherwise be extremely evident, at the expense of picture brightness (necessitating extremely powerful light sources for projection).

24fps is what you’ll see in a cinema, with very few exceptions, but outside of one, all bets are off. You can film at damn near any speed you want, although anything below around 12fps will be distractingly jerky and have very blurred motion. 9,12, 16, 18, 24, 25, 36, and 54fps are common settings on home cameras like Super 8.

As to processing exposed film, you have professional machines like have been described that pull film steadily though various baths, but then you also have simpler devices that can be used at home or for other small scale stuff or when processing is needed in the field. For smaller gauges like 8, 9.5, and 16mm, you can use spiral tanks, which are exactly the same as the ones you’d use to develop still film, but much larger. For something like 35mm I don’t know if a spiral has ever been made for it (it would be mammoth), but you can develop it in a rewind tank. In one of these, there’s a tank with two reels in it. You wind the film onto one reel and connect the end to the other. Then, you add you chemicals to the tank one at a time while continuously winding the film from one side of the tank to the other. And, of course, there’s always the low-tech bucket method (step one: bunch the film up into a big tangled ball; step two: put the ball in a bucket and pour chemicals over it).

True. And when they started compensating for that, it was easy to overdo it; see Gladiator for an example of too much blur making CGI look fake.

Some scenes in Gladiator were so bad that REAL stuff looked fake. For Gladiator, they changed the shutter angle that the film was shot with to give it that stacatto look. Looked fantastic in the early ‘blue’ scenes (watch the snowflakes) but made the REAL tigers look totally fake.

The term used to describe what are mind perceives when viewing a series of varying still images shown in succession is known as “Flicker Flash Fusion”.


Just to add a little detail to the descriptions of shutters: whilst the 24 fps is sufficient to give the impression of smooth motion, it is not fast enough to avoid flicker - try setting your monitor’s refresh rate really low to see what I mean. To compensate the shutter in the projector operates at 48fps, showing each frame twice. Older movies which worked at 16fps would show each frame 3 times for the same reason.

And of course its good old persistence of vision that allows our brain to retain an image(frame or field) long enough to meld it with the next.

Damn. One of the rare threads where I could ramble on from my projectionist days and everybody’s said all of the good stuff :frowning:

Right. The film’s forward motion is driven by a Geneva movement such as the one shown. During the time the film is moving the shutter in the projector cuts off the light so that the motion doesn’t screw up the image on the screen.

Incidentally, it’s interesting to note that the image on the film should look a little blurred (at least for very fast motion), or else things look fake (as wit the tigers in Gladiator mentioned above, although I don’t know if this is why they looked fake. Animation work in films like King Kong and The Beast from 20,000 Fathoms actually looks unreal when the individual frames are too clear – they call it “strobing”, because it looks as if you caught the objects with a strobe light. (Look at the crumbling buildings in Harryhausen’s Earth Vs. the Flying Saucers. Each frame capturwes a bit of stone on its way down, but perfectly photographed, without a blur, because it really is perfectly still as Harryhausen animates it. Real stones, caught on movie film, would be streaks.)

Harryhausen reportedly thought the effect interesting, and didn’t try to fix it. Animator Jim Danforth, anmimating flying creatures, arranged for the wings to move while being filmed, thus giving it a blur. For The Empitre Strikes Back (in some ways, George Lucas’ salute to animation), they used computers to digitially “blur” the image, even in the 1980 release, so it wouldn’t look fake. (Interestingly, they didn’t blur the AT-AT “Walkers”, and the resulting strobing gives the Empire Machines an appropriate mechanical motion. It’s too bad Haryhausen never got to do his version of War of the Worlds, because, judging by this, his tripods would’ve been perfect.) Spielberg had special attachments to the bike models used in E.T. in order to blur the model wheels so they’d look correct during the “flight” scenes.

Go motion.