i see SO many people on here recommending the book Understanding Exposure so I finally bought it and all I can say is WOW. The first few pages put the f/x relation to me mathematically and it all clicked. as the denominator gets bigger the opening gets smaller and you have light levels that need to be matched to iso's and shutter speeds, thus better lenses have smaller numbers, and so on and so on..anyhow GET THE BOOK it is amazing. after one day of reading some much is clearer in my basic understanding. thanks to all who recommended it, you have saved yourself from reading a bunch of NOOB questions!!!