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Resources · Poster · GCSE

Inside a camera

Six cameras cut open: film SLR, rangefinder and TLR above, DSLR, mirrorless and phone below. Follow the light through each one to see how you view the picture before you take it.

Inside a camera poster
Scroll sideways to see the whole poster.

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How to print it

  • At a print shop: give them the print-shop file and ask for A2 at 100%, trimmed to size. Matt paper suits a classroom wall.
  • On a school A3 printer: print both pages of the A3 file at actual size (not “fit to page”), then butt the two sheets together and tape them on the back.
  • For desks: the A2 file prints fine shrunk to A3 or A4 for pairs or groups.

For teachers

What it teaches

  • Every camera is a dark box with a lens, an aperture, a shutter and something that records the light.
  • What changes from camera to camera is how you see the picture before you take it.
  • Film and digital cameras share the same parts at the front; only what records the light differs.

Ideas for a lesson

  • Ask students to trace the light through each camera with a finger and say where it ends up.
  • Compare the film and digital rows column by column: what stayed the same, and what changed?
  • Open the back of a film SLR with no film in it and look at the shutter, then look through the lens with the back open.
  • Give pairs the two A3 sheets and ask them to explain one camera to the class.

Written for GCSE photography; readable from Key Stage 3.

What each camera shows

Single-lens reflex (SLR)

Light comes through the lens and hits a mirror set at 45°. The mirror bounces it up onto a focusing screen, and a pentaprism turns the image the right way round for your eye. When you press the shutter button, the mirror flips up out of the way, the shutter opens and the light reaches the film. Because you look through the lens that takes the picture, what you see is what the film gets, which is why SLRs suit close-ups and long lenses.

Rangefinder

You look through a separate window, not through the lens. A second window a few centimetres away gives a second view of the subject, and in the viewfinder the two views overlap as a double image; turning the focus ring moves one until they line up. With no mirror box, the body is slim and the film sits close behind the lens. The catch is parallax: the viewfinder is not in line with the lens, so close up it frames slightly differently. Many rangefinders help by moving their frame lines as you focus.

Twin-lens reflex (TLR)

Two matched lenses sit one above the other. The top lens is only for viewing: a fixed mirror reflects its image up onto a focusing screen that you look down into. The bottom lens takes the picture, with the shutter and aperture built into the lens itself. The screen image is the right way up but flipped left to right, so following a moving subject feels backwards at first. Most TLRs take 120 roll film and make square negatives.

Digital SLR (DSLR)

Built like a film SLR, with a mirror and a pentaprism, but a digital sensor sits where the film was. Part of the main mirror lets light through to a small second mirror that sends it down to the autofocus sensor. The viewfinder is optical: you see the scene itself through glass, with no screen in between, and you check each picture on the rear screen straight after taking it.

Mirrorless

No mirror and no prism. Light goes straight from the lens to the sensor, which stays on and sends a live picture to a tiny screen inside the electronic viewfinder and to the rear screen. Without a mirror box, the lens can sit much closer to the sensor. Because you are looking at a screen, you can see the exposure before you take the picture, but the screens draw power whenever the camera is on.

Phone

A phone camera works like a very small mirrorless camera: a lens, a sensor and a screen that shows what the sensor sees. The lenses are a few millimetres across and the sensor is much smaller than a camera’s. Most phone lenses have a fixed aperture, so the phone controls exposure with shutter time and ISO, and its processor does a lot of work to make a good picture from such a small sensor.