Gleneagle Secondary

Today, most young people 'snap photo' with their cellphones.  Whether you have a camera or a cell phone, you no longer use a negative.  Your photo today is digital information that you can use in all kinds of different ways: you can instantly email it to a friend, upload it to a website, or edit it on your computer.  Only a few years ago, this  wasn't possible because cameras worked differently: they were entirely analog, capturing pictures as patterns of light and dark using chemically treated reels of plastic film, and a photograph took hours (or even days) to appear in your hand.  Although some professional photographers still use film cameras, most of us have long since abandoned them to history. That's a shame, because they can actually teach us quite a bit about chemistry, physics, and the science of  light.  Thankfully, Gleneagle has a darkroom, which you have all been learning about.  Now let's look at our cameras! 

Much like the human eye, a camera captures rays of light charging in through a lens at the front. But the crucial difference between a camera and your eye is that a camera makes a permanent copy of what it sees. 

what a camera actually does is permanently capture the energy falling on a small, (two-dimensional) surface inside it. In a digital camera, that happens because there's an electronic light-detector chip called a  CCD charge-coupled device) immediately behind the lens, which converts the light energy into electricity.  In a traditional camera, there's no CCD; instead, the incoming energy is captured by a piece of plastic with emulsion on it, that is sensitive to light, better known as the film. The light energy leaves a permanent trace by causing a chemical and physical transformation of the film. (Incidentally, light doesn't just mean visible light: you can, in theory, make a photograph from any kind of incoming light: Infrared, ultraviolet, X-rays ,or whatever you wish.)

How does a film camera work?

The key features of a film camera are:

• A plastic or metal case that is completely light-tight to protect the film.

• An aperture (or diaphragm): a small circular hole in the case that lets in light for the short period when you want to take a photo.

• A shutter mechanism: a spring-loaded set of overlapping blades, like the ones you see at the start of a James Bond film, that open to let light in through the aperture for a precise amount of time before closing up again.

• One or more lenses in front of the shutter. The  lenses are a crucial part of the camera and do several jobs at once. First, they scale down the large, incoming image of the world so it fits into a much smaller area of film: no-one really wants life-sized photos! Second, lenses concentrate the incoming light energy so the image forms on the film more quickly and the camera can be used in darker conditions than would otherwise be the case. Third, they bring the light rays into a sharp focus exactly on the surface of the film, so you get a clear, sharp, image rather than a blurred, fuzzy impression. Finally, they also minimize the distance between the aperture and the film so cameras can be made relatively small and portable. When you adjust the focus on a camera, you're actually moving one or more of the lenses back and forth (closer to or further from the object and the film) to make different parts of a scene appear sharper on the film, according to whether you want to emphasize near or distant objects in your photograph.

• A roll or piece of film (on the back wall of the camera directly opposite the shutter).

• Photographic film is plastic (or sometimes paper - like with our pinhole cameras) that's coated with an emulsion made from microscopically tiny crystals of silver salts suspended in gelatin (a jelly-like substance found in sweets such as wine gums). The silver salts are compounds of silver and halogens such as chlorine, iodine, and bromine, also called silver halides—and their useful feature is the way they begin to change into pure, metallic silver when light falls onto them. If lots of light hits them, they change much more dramatically than if less light hits. This is how the two-dimensional pattern of light rays entering through the lens of a camera from the world outside forms a kind of invisible, chemical trace (called a "latent" image) on the surface of photographic film.

• To turn your negative into a recognizable photo, you have to develop the film in a darkroom (usually lit with red or green light that doesn't affect the film). This involves dipping the film in a series of chemicals, which convert the latent image captured by the tiny silver halide crystals into a visible image formed of larger silver particles, and also makes that image permanent.

• First, the film is dipped in an acidic solution called developer, which encourages more of the silver halide to convert to metallic silver and renders the latent image visible. To stop this process continuing indefinitely, and ruining the photo, the film then has to be dipped in an acidic solution called a stop bath to neutralize the developer. Once that's done, the image is made permanent by dissolving any remaining silver halide using a chemical solution known as hypo (or fixer), before being rinsed clean in water and hung up to dry.

• At this stage, the image, though visible, is still in a negative pattern, with light areas looking dark and vice versa. That's why developed pieces of film are called negatives. Once the film is developed, it's printed: this is where you shine a light through the negative so it casts a shadow onto photo-sensitive paper and turns the negative film into a recognizable photograph called a (positive) print. You can make any number of prints from a single negative, which is one of the great advantages of this slightly laborious, "positive-negative" photographic process. By adjusting the distance between the negative and the paper you're printing on, and using lenses, you can also enlarge or reduce the size of a an image. The piece of equipment you use to do this is called an enlarger.

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