Camcorders and movie cameras

Last updated: March 11, 2008.

Ordinary cameras are brilliant for taking snapshots of the world. The only trouble is, the world simply won't "sit still"—there's always something moving around us, over our heads, or even under our feet! Fortunately, movie cameras are able to capture moving images that better reflect the changing nature of our world. Compact movie cameras called camcorders are small and portable enough to take anywhere and, because they use digital technology, you can easily edit the films they take on your computer and even upload them onto the Web.

Photo: When something as specactular as an aircraft carrier (USS John F. Kennedy) passes nearby, you won't want to miss the action either! Photo of a Sony/Panavision by Jim Hampshire courtesy of US Navy.

"Persistence of vision": How the eye fools the brain

Open up a camcorder and you'll find all kinds of mechanical and electrical parts packed inside. But the basic science behind making movies has nothing to do with lenses, gears, electric motors, or electronics—it's all about how our eyes and brains work.

You've probably done that trick where you make a flip book by drawing little stick people on the corner of a pad of paper and flicking them with your fingers so fast that they hop, skip, and jump. When your eye sees a series of still images (or "frames") in quick succession, it holds each image for a little while after it disappears and even as the next one starts to replace it. In other words, each picture leaks into the next one, so they blur together to make a single moving image. This is known as the persistence of vision and it's the secret behind every movie you've ever seen.

It's not just flick books that use persistence of vision. Before movie cameras and projectors were invented, 19th-century toy makers were using the same idea to make relatively crude animated films. A typical toy from this era was called the zoetrope. It was a large rotating drum with thin vertical slits cut into its outer edge. Inside, you placed a long strip of paper with small colored pictures drawn on to it. Then you rotated the drum to make the pictures blur together (just like a flick book) and looked down through one of the slits to watch them. Here's a great photo of a restored zoetrope by Andrew Dunn.

How movies work

It's a relatively small step from flip books and zoetropes to fully fledged movies. The theory of making a movie is just as simple: you take thousands and thousands of still photographs one after another. When you play them back at high speed, they blur into a single moving image—a movie.

A famous American photographer called Eadweard Muybridge (1830-1904) was one of the first people to show how one moving picture could be made from many still ones. Using multiple cameras arranged in rows, he took series of photographs of galloping horses and vaulting gymnasts. Few things illustrate how movies work better than Muybridge's amazing photos. Here's a sequence he made called horse in motion:

Photo courtesy of US Library of Congress.

How movie cameras work

A movie camera or camcorder simply automates what Muybridge did by hand. A basic movie camera is like a standard film camera that takes a photograph on to plastic film every time the shutter opens and closes. In a standard film camera, you have to wind the film on so it advances to the next position to capture another photograph. But in a movie camera, the film is constantly moving and the shutter is constantly opening and closing to take a continuous series of photographs—about 24 times each second. Before camcorders were invented, people used mechanical home movie cameras, which were very small versions of professional movie cameras with all the parts (and the film itself) miniaturised. When video was invented, photographic tape was replaced by magnetic videotape, which was simpler, cheaper, and needed no photographic developing before you could view the films you'd recorded. Mechanical movie cameras soon started to evolve into convenient, modern, electronic video cameras.

Photo: At first glance, this old-style Arriflex film camera looks quite like a modern camcorder—but look closer. On top, you can see a big oval-shaped case where a huge reel of film is stored. If you were standing next to this camera, you would also be able to hear a motor inside whirring away as the film rattled through the mechanism. Photo by Dave Maclean, courtesy of Defense Visual Information Center.

Modern camcorders use digital video. Instead of recording photographic images, they use a light sensitive microchip called a charge-coupled device (CCD) to convert what the lens sees into digital (numerical) format. In other words, each frame is not stored as a photograph, but as a long string of numbers.

So a movie recorded with a digital camcorder is a series of frames, each stored in the form of numbers. In some camcorders, the digital information is recorded onto videotape; in others, you record onto a DVD; and in still others, you record onto a hard drive or flash memory. The advantage of storing movies in digital format is that you can edit them on your computer, upload them onto web sites, and view them on all kinds of different devices (from cellphones and MP3 players to computers and televisions). Try doing that with a silent movie from the 1920s!

Photo: Left: A Canon XL1S digital video camcorder in action. Note the boom microphone on top for recording high-quality sound. You focus the image by turning the lenses at the front with your fingers. Photo by John A. Lee, II by courtesy of Defense Visual Information Center. Right: The same camera front a slightly different angle. Photo by Kristi Mulder by courtesy of Defense Visual Information Center.