Question: How does a camera take a picture.

Louise Dash answered on 15 Jun 2010:

In a film camera light coming through the lens reacts with chemicals in the film (silver halides) so that when it’s processed in a darkroom the bits that have been exposed to light get dark, while the bits that haven’t get washed away – this gives you a negative image. You can then (again in a darkroom) shine light through the negative image onto photographic paper which uses the same silver salts. This is processed using chemicals so that now the dark bits on the negative make light bits on the paper, and vice versa, to make a positive image.

In a modern digital camera there’s no “film” and no chemical reactions – instead of the film there’s an electronic sensor so that when a particle of light (called a photon) hits the sensor it generates a tiny electric current which the camera processes and records on a memory card. In fact the sensor is divided up into tiny areas called pixels which each register the amount of light separately – my camera has 10 megapixels, or 10,000,000 little sensors each recording how much light hits them, which is then used to build up the picture.

A digital camera records colour by using filters over the sensor – so some pixels record the amount of green light, some blue, and some red (because if you mix green, red and blue light you get white light!) In fact there’s twice as many green pixels as there are red or blue, because the human eye is more sensitive to green light than red or blue.

Photography is one of my hobbies 🙂 and I think it’s fascinating how we can use light to capture images! When I was at school I did some film photography and used to love messing around with chemicals in a darkroom, but it takes a long time. It’s much easier with a digital camera where you can see what your photo looks like straight away!