How Does a Camera Work?

Meet John Tregerthen Short. Doesn’t he look like a grumpy old sod?

There are two potential reasons for said grumpiness. The first is that John Tregerthen Short really was just a grumpy old sod (I wouldn’t want to rule it out), but the second explanation is a little more scientific and requires a short digression into exactly how a camera works.

A camera is essentially a dark chamber which lets in a bit of light. The size of the chamber can vary astronomically. The first “cameras” were simply house-sized dark rooms with a small window. You wouldn’t be too far off if you thought of this window as a lens and because the only light source in the chamber came through this lens, an outside image could be projected onto a paper sheet and then the outlines traced by an artist.

This clearly was far from ideal and great effort was made to produce a way to store these images more permanently. So the paper upon which the image was projected was replaced with a metal sheet: a tin and copper alloy which had been impregnated with chemicals such as bitumen, lavender-oil and silver nitrate. This early concoction of chemicals darkened according to the intensity of light they were exposed to, creating a ghostly negative image. Further treatment of this negative image produced a photo.

The problem with this early method of capturing a photo was two-fold. The first problem was that for a photo to imprint onto the impregnated metal plate, sufficient light had to be captured and bent through the lens and the lenses simply weren’t big enough. The chemicals weren’t really up to the job either. The light-sensitive silver halide crystals used today, which are capable of an almost instantaneous blackening as they decompose to silver metal, are much more efficient at capturing an image than the concoctions of times gone by. Together, unsophisticated lenses and unperfected chemistry meant it might have taken an understandably sullen John Tregerthen Short as long as twenty minutes to have his photo taken! This is almost as unbearably long as a post-Corp Snapchat story.

Credit: Bill Ebbesen

Analogue cameras of today use a plastic film rather than a metal plate and the tiny silver halide crystals are mixed with gelatine, which suspends the crystals in an emulsion. However, they function in much the same way as early cameras. When you press a button, the shutter opens producing an aperture, light pours in through the lens, reacts with the halide crystals and imprints the image onto the gelatinous film, which can then be taken to Boots to process the negative image (self-confessed hipsters with polaroid cameras can forego this last step as the camera contains a negative film).

Digital cameras work a little differently since they contain no film and thus no gelatine. This incidentally means that unlike analogue photography, digital photography is vegan-friendly. In place of a film there is an amazing piece of electronic equipment called a charge-coupled device (CCD). A CCD captures incoming rays of light and converts them into electronic signals. The incoming picture which hurtles through your lens bashes into the CCD, which breaks it into millions of pixels. Each pixel is then individually analysed by the CCD. It looks at the brightness and colour of each pixel and saves this as a number.

This means that that shameful selfie that you accidentally sent to your mum, that adorable photo you snapped of your new cat, Marsha, and that annoying picture of Kim Kardashian that keeps popping up on your newsfeed are, when it boils down to it, just an enormously long string of numbers describing component pixels.

I’m sure if John Tregerthen Short could see that, he’d crack a smile.

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