Learn the history of the 35mm film projector and how it works.
When you go to the movies no matter how engrossing the scenes are, you know that they are not true. You know that those are not real dinosaurs on the screen, that they are in fact a trick on your eyes. Did you ever stop to think though that the entire process of film is a trick?
The motion picture business, at its core, is based on a theory called "˜Persistence of Vision'. This is the scientific theory that the eye can retain an image for 1/20th of a second after it sees it. With this knowledge, you can run a series of successive still pictures past the eye and make it appear that the image is smoothly producing movement. (As an example: Take a picture of a person with their arms in the arm, another picture with the arms at their eye level, than an image of the arms at the chest, below the chest and then resting at their side. When all of these images are run past the eyes in a rapid, successive matter it appears as if the person (in one fluid motion) swings their arms from the top of their head to their side.)
In 1834 William George Horner took this theory of the Persistence of Vision and used it to build a Zoetrope. To easily describe a Zoetrope think of a coffee can with its lid off. Affix a pole to the bottom of the can so that it can easily spin the can around, then cut holes in the sides of the can, large enough so that you can look through them and view the paper strip of images that has been glued to the inside. Then the can would be spun and one would look through the side to watch the image inside "˜move'. This was not the only way to watch a moving picture but it was the best way until 1891 when Thomas Edison produced the Kinetoscope. The Kinetoscope was sort of the "˜hi-tech' version of the Zoetrope. It used a motor to revolve a film loop in front of a light source that then projected the image in a booth. This was an important step because it projected film mechanically, into an area where people could enjoy it in a public setting. It soon became apparent that people would not only gather together to watch films, but that they would pay for the chance to do so as well. This spawned a number of kinetoscope imitations (including a few by film pioneers the Lumiere Brothers). In 1896, the next big advancement was made with the invention of the Vitascope. The Vitascope worked in essentially the same way that the Kinetoscope did with its difference falling in the fact that it's image was projected onto a large screen. This really paved the way for what is widely credited as the first film theater, the Nickelodeon in Pittsburgh, PA. Inventors continued to toy with film and its projection until they reached what we have come to know as the modern film projector, although it too is consistently adapting and evolving. Where it will go in the world of digital filmmaking is still anyone's guess.
For our purposes, we shall look at the workings of a 35mm film projector. Even a standard projector is quite a technical accomplishment and to really do its description justice, we would need more space than we have. So we will take a basic look at how an image makes it onto the silver screen and even in this brief look, you will gain a little more respect and knowledge for what goes on in that little room in the back of the movie theater.
The first thing you need for a movie projector is of course the movie. A projector moves 24 frames per second in front of its lens. These are decent size frames and it actually takes 16 frames to make up a foot of film. Doing the quick math tells you that those 24 frames take up 1.5 feet of film. Carrying this further you can quickly see that one minute of a movie is equal to 90 feet of film while a typical two hour movie (plus previews) can regularly clock in around 2.13 miles of film.
To hold all of this film, a projector is set up next to platters. As a minimum, you need two platters, one to feed and one to take up. The complete film is laid flat on the feed platter, runs through the projector and rolls it's self back up on the take up platter. The beauty of platters is that when a movie is over, the take up platter switches rolls to become the feed platter and the process repeats. Today the majority of movie theaters use platters, however older art houses and independent theaters still use reels. In a reel projection system, a film would actually be shown on reels. This would require two projectors per screen. The film would run through the projector on a reel and when it was nearing the end of the reel, a small symbol or cigarette burn would appear in the top right of the screen. This would alert the projectionist to start the second projector. These can still be seen today even at movie theaters that employ platter projectors. The second projector would then begin as the first one's reel reached the end. That projector would have reel three put on it and the process then continued.
To a projector, what's important is not the actual image on the film but instead the sprockets which line the side because the projector uses these sprockets to pull the film through itself. The film is threaded through the film with the sprockets aligning themselves to a series of spring loaded rollers which provided needed tension to keep the film from slipping. Film does not roll through a projector continuously, rather it advances one frame at a time. Projectors use either a claw or intermittent sprocket to perform this task. Once the film makes it to the lens, it gets its image to the screen thanks to the powerful light of Xenon bulbs. Xenon is a gas that provides amazing illumination for prolonged periods of time. The bulb sits in the middle of the lamphouse which could also be know as "˜The House of Mirrors' because of the mirrors inside which help to focus the bulb's light.
This light rockets out of the lamphouse to the shutter. This is a small "˜plate' that spins around 24 times a second. It lets the light get to the film, rotating in such a way to eliminate jerky movement and flickering on screen. The light must also get past the aperture, this is a small frame that makes sure the light only hits those areas of the film that should be seen on screen.
Now the image is finally ready to go to the lens. There are two types of lenses: Flat and Scope. The easiest way to explain a difference between these two is that Flat is more of a small, family drama while Scope is a large action picture.
From a spinning can to the doorstep of digital, movie projecting has grown a long way. It will be interesting to both movie watches and moviemakers to see what the future holds.
