I once heard of a newspaper photographer colleague who, when asked what camera settings he was using replied "Its set to P - for Professional". I thought this was hilarious (still do). "P" simply stands for "Program Mode" which is the fully automatic exposure mode on most camera models.

The latest auto-everything, all-singing, all-dancing, digital cameras are amazing. They're basically powerful computers with a lens attached and can work out exposure and focus for you without you having to really understand the basic principles. And they can do this so quickly that they can record millions of pixels of information at the rate of (for my camera) 10 pictures every second.

So why not just set the camera to "P" and fire away?

Because the camera is not always right.

There is a case for arguing that there is no such thing as a "correct" exposure. Only the exposure that renders the scene the way you, the photographer, want it to look. If you stand someone with their back to the sun and shoot a silhouette, is that the correct exposure, or is the person dramatically underexposed? Well, its both. Its up to the photographer to decide whether the person will be a black silhouette against the background, or whether the details of the person should be correctly exposed and the background dramatically overexposed. Or... you could use flash to balance the two elements.

The camera cannot decide this for you.

Contrary to what most consumer oriented camera advertising will tell you, even the latest and greatest hi-tech camera cannot know what it is you are trying to photograph. It can guess, based on an internal database of average picture types, but then most photographers would rather their pictures were better than "average".

(And don't even get me started on things like "Portrait Mode", "Landscape Mode", "Sports Mode", "Night Mode" ....)

Its vital for any photographer to have an understanding of the principles of exposure, focus, composition, depth of field, focal lengths and perspective. The photographer should be able to look at a scene and know what the final picture is going to look like with the lens and camera settings chosen. Whether the camera chooses the settings automatically, or the photographer chooses them manually, the final decision on what is "correct" should be the photographer's.

I've always shot the vast majority of my work using manual exposure, using the camera's built in metering to help me make the decision. This way I know what the camera is doing at all times. Sometimes I might get it wrong, but I'll only have myself to blame - not the equipment.

Oh, and there are two other things the camera will never be able to help you with - what to point it at and when to click the shutter.