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How do Film Reels Work?

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By Elaine Elliott

Due to the convenience and affordability of digital photography, nearly all modern movies use digital cameras and digital movie projectors. A handful of directors such as Steven Spielberg and Wes Anderson still encourage film stock, but it adds a big dent to the film budget. 

Even if digital convenience now dominates the film industry, film reels were how movies were shown on the big screen for decades before. 
So how exactly do projectors and film reels work?

 

Before we get into a spiel about projectors, let’s start with how images are laid out on film in the first place. Photochemistry is the science behind layering images onto film. About 20 thin layers are coated together on a single film square using gelatin to hold the layers together. The images have tiny silver-halide crystals to detect photons. Organic molecules on the surface of the film transfer the color and light to the crystals through photoelectrons to create the image.

 

When the silver halide grains on film change color when interacted with light, an image can pop onto a screen even though they were difficult to make out on the actual filmstrip.

 

35mm filmstrips are the Hollywood standard, but there are also other sizes like 8mm, 16mm, and 70mm.

 

Audio can be synced to a film using magnetic or optical waveform strips on the side of the filmstrip’s perforations (the black edges of film). But keep in mind, audio is still recorded to a separate device.

 

Once a movie is completely transferred onto film, it’s time to reel it through a projector. Every second of a movie requires 1.5 feet of film. That means an hour long movie requires over a mile of filmstrip!

 

Film reels help separate these film lengths from getting messy or disorganized (remember when a VHS tape broke and you were left with a tangle of film?!). A two hour feature film is usually divided into five or six reels.

 

Projectors seamlessly thread all this film through a mechanism that reveals the film onto a screen. Projectors were built to work alongside cameras, and thus the technology is very similar.

 

To start, the film is moved from the supply reel (a storage base for pending film), then it moves through the lamp and lens (to project the images), then the sound drum, and finally collected on the takeup reel.

 

A “shuttle” moves the film from frame to frame without moving the film itself to avoid blur. The shuttle is extremely fast, and moves about 24 frames per second. Along with the shuttle, the shutter mechanism moves once per frame to fully eliminate additional blur.

 

A very bright light placed right next to the lens is necessary for making the images visible. That’s why you can see a glaring light at the back of every theater in the projection room.

 

Movie scenes are placed on film in translucent images that the projector’s lamp can shine through to project the pictures onto a screen.

 

Once film platters were invented in the 1960s, projectionists no longer had to physically change out reels during a movie. Instead, the payout assembly feeds film from one side of the platter disc to the other. The projectionist would splice together the film reels by taping the end of one film reel strip to the other. Now one projector could show an entire movie!

 

Films became more affordable to manage, and projectors could start showing multiple movies at one time (which lead to the trend of multiplex movie theaters).

 

In the 1990s, movie theaters started transitioning from 33mm film projectors to digital video projectors. In 1998, The Last Broadcast was the first movie completely shot, edited, and distributed digitally.

 

Some movies are still shot on film, and produce the same quality as digital. But the reign of film is slowly becoming less and less prominent. 

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