Camera Basics

How a camera Works …how the heck does a shoebox take a picture? All the objects we see, or photograph, reflect light in many directions at once. Every part of that object, no matter how small, reflects countless rays of light. The light rays are disorganized and scattered, which is why film alone can’t form an image.

To create a photo you need a way to collect and control the rays of light entering the camera. This is the job of a lens – a cylinder of glass at the front of the camera. A lens does two main things. It creates a sharp (or in focus) image of your subject , and it makes it possible to use a larger opening to let more light into your camera – while still creating a sharp image.

This means that your exposures can be faster. Think about your pinhole cameras – because the hole is so small, very little light can travel through it, so our exposures are very long. We can make the hole bigger, but without a lens, our pictures would be blurry!

Getting a lot of light to the film in a very short time (a 500th of a second for example) means: That moving subjects can be photographed without producing a blurred image. That pictures can be taken in lower light. That a camera may be held by hand for a photograph, rather then supported in a fixed position (our pinhole cameras have to be resting on a stool – even when we are shooting outdoors!).

When you Take a Picture: Light passes through the lens and hits a mirror (green) The mirror reflects the light up to a focusing screen The light passes through the focusing screen and enters the pentaprism - a block of glass with five sides (orange)

The pentaprism corrects the upside-down and reversed image, so that when we see the dog's image in the viewfinder eyepiece, it's the right way up. When you take a photo, the mirror flips up and a shutter (blue) opens that exposes the digital sensor or film to light