Science In Real Life

In a world where science is taken for granted, mistreated, and just plain misrepresented … one man will take a stand. One man will fight for learning, for education, and for the Universe. And along the way, he will discover that the science he fights for surrounds us all. That man … well, that man is me, and this essay marks the beginning of a new venture here at Science in Real Life, wherein some of my essays will take the form of movie reviews, of a sort. Rather than discussing the movie on its artistic or literary merits, I will be expounding on the science it contains, both explicitly and implicitly. Partly I do this to call attention to and correct any bad science I find in popular movies, and I will not deny that I take a certain vindictive pleasure in demonstrating how truly idiotic some cinematic depictions are. But I also do this because some movies get it right, or mostly right, and these deserve not only praise but recognition and explanation, the better to help you, dear readers, develop a scientific intuition.

The filmgoing fun will begin in earnest next week, with some of the holiday releases, but for now we’re going to have a look at the science that makes it all possible: movie projection. Leaving aside certain thorny philosophical questions about the nature of space and time, your eyes perceive motion by recognizing a similar shape from one position to another. While your eye has no inherent frame rate, since it does not work by taking snapshot images, your brain is so good at filling in the gaps to approximate the sensations to which it is accustomed that it will register smooth motion at anything above 16 frames per second. Movies are typically projected at 24 fps, television at 60 fps, and Spongebob Squarepants at roughly five million.

( Image Credit: Paramount Pictures )

Some of you at this point are thinking of the old zoetrope, wherein a cylinder of images is spun to create the illusion of a moving picture.

( Image Credit: Encyclopedia Britannica )

This, essentially, is what is happening when you plop yourself down at the local multiplex for the latest Saw movie. The key element here is that we see the individual frames, but not the transition between them. In a zoetrope, the fact that you are constrained to look through the slits means you only see each image when it is directly in front of you, not moving in or out of “frame”. A cinematic projector, to accomplish this, has a shutter that opens and closes in synchronization with the switching of the frames on the film reel. But, like an eager dog that goes back and forth 2 meters for every meter her owner walks, the shutter in cinema projectors is operated at 48 Hz or 72 Hz, to the film’s 24. This is done to reduce the appearance of flicker on the screen, since every time the shutter blocks the light, the screen goes dark. In computer terminology, that 72 Hz is the refresh rate of the display. Compare that to the 200 Hz refresh rate common to most LCD monitors and one wonders that movies seem so fluid.

Of course, merely shining a light through the film is not enough. A lens is required to bend the light to fit the size of the screen, and an aspect mask is required to fit the proportions. Movies are typically shown in a 1.85:1 ratio of width to height. In the old days before HD television, most TV sets were 4:3, or 1.33:1, which is why you always saw the screen that said “This movie has been formatted for your television.” The TV station had to adjust the film or else you’d only be seeing half the movie, and Star Wars just wouldn’t have been the same without the dark side.

Speaking of the film, the substance itself has a complex chemistry behind it, the full details of which are beyond the scope of this essay. The short version is that these days what you have running through a projector is a strip of polyester base (yes, just like your gym shorts) coated with layers of silver halide grains emulsioned into a gelatin (just like your mom’s cooking). Each layer has a dye in it corresponding to cyan, yellow, and magenta – et voila, color film. All of this is transparent enough for light to shine through it, and colored enough to filter the light that passes through into the desired image.

Well, there you have the very basics of movie projection – I wanted to discuss 3D movies, but that can wait for one of this week’s Science Bites. Tune in next week when Science In Real Life tackles Avatar, one of the most science-heavy movies to come out of Hollywood since Science: The Movie.