How 35mm Cameras Work

How to Use It

35mm cameras are named for the type of film they use---35mm; also called "135 film," it measures 35mm in width. 135 film comes housed in a light-proof, cylindrical case and generally contains enough length for 36, 24, or 12 exposures, with each exposure measuring 24mm x 36mm.
A button or release, typically on the side of the camera, opens up the film compartment. Insert the 35mm film canister into the grooved cavity, feed some film across the shutter and into the opposite side, and close up the compartment. Wind the "film advance lever" (if your camera has one) and you're ready to shoot.

When you look through the viewfinder of a camera, the image that you see is the result of light being filtered through the lens. Inside the lens, glass elements focus the light into a tiny beam that shines into the camera. The beam of light strikes an angled mirror, reflecting upward and through a prism that filters it into a viewable image for the viewfinder.
When you press the shutter-release button to take a picture, it activates a rapid series of events within the camera. First, a device within the lens, called an "aperture," partially closes to control the amount of light that enters the camera, preventing "overexposure" of the film. Next, the angled mirror lifts out of the way, creating a short moment of darkness within the viewfinder. Then the shutter quickly opens and closes, briefly exposing the film to the light. The mirror and aperture then return to their normal positions.
As light hits the film, it activates a "silver halide salt" coating, converting it into metallic silver, which forms an inverse of the image upon the film (the picture is reversed to its proper form when transferred from film to photo paper). In color film, dyes within the silver salt are activated to create the coloration.

35mm cameras come in many different styles---however, most fall into one of two categories: point-and-shoot or SLR. The physics of operation are almost identical between the two. The main difference is the amount of control afforded the photographer.

A classic point-and-shoot camera.
A point-and-shoot 35mm camera works just how it sounds: You point it at something and take a picture. These cameras are usually fully automatic and do not require you to wind the film or focus the lens. When you take a picture, the camera automatically chooses an aperture setting, or "f-stop," and "shutter speed" (determines how long the shutter stays open), depending on light conditions. However, the range of f-stops and shutter speeds in a point-and-shoot are usually quite limited. Many of these types of cameras come with a flash to aid the limited aperture and shutter in low-light conditions.

An SLR camera
An SLR (Single Lens Reflex) camera gives the photographer more control over the aperture and shutter, as well as the ability to manually adjust the focus. You can set the shutter speed at a number of different settings, controlling how long the film is exposed. You can also adjust the size of the aperture by changing the f-stop, although the amount of available f-stop settings depends on the type of lens. By adjusting both the shutter speed and aperture you can control the exposure and contrast of your picture. Most SLRs have a light meter inside the viewfinder to help find the right setting. An SLR may also use a flash, but with the extra amount of control, it is not needed as often as in a point-and-shoot. Most modern SLRs include both manual and automatic settings.