f stops and ISO!

I am desperate to understand the more technical side of my camera and take better photos. I have tried several on line tuts, forums and books but am still struggling. Yet I really want to get to grips with some of it at least before I go away. So in a mad rush of blood to the head, (and to escape somewhere out of the cold while shopping) I dived into the library on Monday and ended up taking out two books on photography.

The rather hefty volume I haven't looked at, it looks like the normal technical ramblings that tend to go straight over my head but the pictures looked good, but the second is a little different. Its by Jon Cox, an American teacher/free lancer and the book is called 'Digital Nature Photography'. There are some stunning shots in it, but more than that it is very readable and IT EXPLAINS stuff!

Alright I have only got to page 31 and the first chapters were all on choosing equipment and filters, lenses etc., but I have just come across the most brilliant and best explanation of f stops/ISO numbers that I have ever read. So I want to put it down here so that when the book goes back to the library I still know what its all about, and because I think its worth sharing.

So basically he says that a stop is a way of measuring light, but to make it easier to grasp think of it in terms of travelling. If you travel a mile it doesn't matter if you go by bike, train, foot, horse or car, its still a mile whichever way you go. So if you 'travel' one stop of light with your camera it doesn't matter if you use the shutter speed, the f stop or the ISO you still only move 1 stop. Now why cant the other books have said that instead of waffling on about how you need to know your camera and change one or a combination and yet never tell you which or how?

His other explanations have been just as useful. He talks about situations that you can envisage, for instance the need to change ISO in order to capture more light if hunting a shot of an owl in a dark dense forest. And he is the first person I have ever come across who has explained that each doubling or halving of the ISO number is the same as one stop of light, so that moving from ISO100 to ISO200 is one stop and from ISO100 to ISO 800 is three.

Now all I need to do is find my camera manual to work out how to change ISO in the first place LOL