Your Questions: Answered – Cameras

Please explain how cameras work, like from old fashion camera’s to the modern digital ones we use today. It blows my mind! – Kristoffer Stewart

A camera, at its most fundamental, is a device that captures and stores images.  Cameras have evolved a lot over the years and when you stop to think about what our modern cameras can do, it does seem kind of like magic.  But rest assured, it’s science! What follows is a brief history of the camera, from 400 BCE to present day

Camera Obscura

The first instance of the camera, and in fact the origin of the word itself, is from the camera obscura.  The word “camera” is latin for room and “obscura” means dark.  The principle is quite simple and was applied as early as 400 BCE in China to impress emperors.  When a small hole is made in the wall of a dark room, the light that shines through will produce a reversed image of whatever is on the other side.  These devices/rooms became popular in the middle ages and there’s even one on the roof of a popular tourist attraction on the Royal Mile in Edinburgh.

Camera_obscura2
A demonstration of the principle.

Photographic Plates

In the late 1700s and early 1800s, it was discovered that certain chemicals, like silver chloride or oil-coated pewter, darkened when exposed to light.  By placing plates covered in these materials on the screens of dark boxes with pinholes, it was possible to record images without having to trace them.  Chemicals that darkened when exposed to light were preferred to those that lightened because a negative can be used to create unlimited copies. Over time, more sensitive chemicals were added, cameras became more portable, and lenses were added to give crisper images.  The standard format of this era (mid 1800s) was the daguerrotype.  It was a very expensive and time-consuming process, but gave fantastic results.

Image by Susanna Celeste Castelli, DensityDesign Research Lab
Image by Susanna Celeste Castelli, DensityDesign Research Lab

Film

Eventually, plastic film replaced solid photographic plates.  Plastic coated with a mix of gelatin and microscopic crystals of silver halide was fed into the back of cameras.  This had the advantage of being much cheaper and more portable.  The first films had the disadvantage of being quite flammable and dangerous.  They were eventually replaced by safety film.  Kodak can lay claim to selling the first commercially available film camera.

This is an ad from 1900.  I wonder how much one of those would go for today...
This is an ad from 1900. I wonder how much one of those would go for today…

Film cameras continued to get smaller, with better lenses and more control over parameters like aperture and shutter speed.  The disadvantage with film is that it needs to be processed (the negatives produced by taking exposures must be passed through a series of chemical baths in a darkroom) and the results of the adjustments you may have made aren’t immediately obvious.

Digital Cameras

In order to solve that very first-world of problems, enter… the digital camera! The only difference between the cameras discussed above and a digital camera is where the light goes to imprint its image.  Instead of a wall, photosensitive plates or photosensitive plastic, digital cameras have charge-coupled devices (CCDs).  These are small squares of silicon that build up a small, local electric charges relative to how much light is striking them.  CCDs are divided into many (sometimes millions) of smaller sections called pixels.  Each pixel is bounded by a small strip of metal (usually aluminum) and an indent.  The brighter the light that is striking a pixel, the more charge it will build up.  The charge is then moved, row by row, to a reader at the bottom of the CCD that turns the charge into a digital signal and stores it to the camera’s memory. CCD Effectively, all that’s happened is that we’ve replaced a chemical process with an electronic and digital one. Watch this video for a tidy explanation of how CCDs work.

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