Camera Exposure - Getting it right

In photography, 'exposure' means the amount of light that falls onto the film, or CCD if you are using a digital camera. In modern cameras the exposure is usually set to automatic by default and, most of the time, it can be left there and will produce beautiful pictures. There are times though, when the lighting conditions are difficult or we want to produce a particular effect and it would be nice to understand what is going on 'under the hood'.

The problem with all types of film and recording media is that they cannot record the entire range of contrast (black to white) that the eye can see. Especially when you take into account that the eye is constantly adjusting to cope with high contrast. On a sunny day if you look into the shadows of a scene then into the bright areas, the iris in your eye will quickly adjust so you can see detail in both.

Faced with the task of recording as much information as possible, the camera will try to average out all the light levels and expose the film accordingly. As burnt out highlights are normally considered uglier than black shadows, the camera, left to it's own devices will normally err on the dark side. Which is no good if you are shooting someone's face against a bright sky. It's the person's face you want to see, and you don't really care if the sky is white.

Auto Exposure
The camera manufacturers have come up with all sorts of ingenious metering systems to try to help, there are now multi mode metering systems, which give you a choice of 'center weighting', 'spot metering' or 'multi spot metering' on many of the better cameras, but none can guarantee to give you what you want every time.

The temptation to think that your camera 'knows what it's doing' is great, even for more experienced photographers, which is my main complaint against automatic cameras. It's easy to get lulled into a false sense of security, switch your brain to more interesting things and end up with a pile of rubbish.