In a movie theater, you watch an image projected onto a screen. How is that done? ​ 

Projecting the Best Image 

Have you ever made a pinhole camera? If you have, you were projecting an image onto a flat surface. The image was small, dim, and upside down. The projector at the back of the movie theater is similar, but it is a more complex optical device. It uses a very bright light source and lenses to project a big, bright image onto a screen.

Historically, all movies were recorded on film. The film—a long strip of translucent images—is positioned in the middle of a movie projector. Behind the film is a very bright lamp sitting inside a concave reflector. White light from the lamp is concentrated though two lenses— called a condenser—onto the film. The rays emerging from the condenser pass through the film. The images on the film act like a series of multicolored filters. The filtered light, carrying the image on the film, then passes through a series of lenses that spreads the light out and focuses it onto the movie screen. When the light strikes the screen, the image produced is therefore many times larger than the original tiny picture on the film. The movie screen then reflects the light that forms this image back to your eyes.

How do we see moving pictures on a cinema screen?

To understand how we see moving pictures on a cinema screen, we need to delve into the process that occurs behind the scenes. Here's a detailed explanation of the steps involved:

1. Film Production:
- A film is created by capturing a series of individual frames. Each frame consists of a still image that represents a single moment in time.
- The frames are captured using a camera, either on traditional film or digitally.

2. Film Editing:
- After the frames are captured, they go through a process called film editing.
- In film editing, the individual frames are arranged in a specific order to create a coherent story or narrative.
- Additionally, special effects, sound effects, and music may be added during this stage.

3. Film Projection:
- Once the film is ready, it is transported to cinemas for projection.
- The film is loaded into a film projector, which is a specialized device designed to display motion pictures.

4. Film Projection Process:
- The film projector has several components that work together to display the moving pictures on the cinema screen.
- The film projector consists of a light source, a film reel, a lens, and a screen.

5. Light Source:
- The light source in the projector, typically a powerful lamp, emits a strong beam of light.
- This light passes through the individual frames of the film.

6. Film Reel:
- The film reel holds the film and feeds it through the projector.
- The film is pulled through the projector at a constant speed, typically 24 frames per second.

7. Lens:
- As the film passes through the projector, it goes through a lens.
- The lens focuses the light that passes through the film onto the cinema screen.

8. Cinema Screen:
- The cinema screen is a large, flat surface that is specifically designed to reflect the projected light towards the audience.
- The moving images are displayed on the screen, and the audience can see them.

9. Persistence of Vision:
- When the individual frames are projected onto the cinema screen at a high speed, typically 24 frames per second, our brain perceives it as continuous motion.
- This phenomenon is known as persistence of vision.
- It allows us to see the series of still images as a smooth, moving picture.

10. Sound System:
- In addition to the visual display, cinema screens are equipped with sound systems to enhance the movie-watching experience.
- The sound system synchronizes with the projected images, providing audio to accompany the visuals.

In summary, the process of seeing moving pictures on a cinema screen involves film production, film editing, film projection, the use of a light source, film reel, lens, cinema screen, and the phenomenon of persistence of vision. This combination of elements creates an immersive cinematic experience for the audience.