was a camera nerd for a brief period of time when my first daughter was a baby (been a while)...F stop (or aperature) controls the amount of light entering the camera as well as the depth of field that is in focus. Setting it one way (can't recall low f stop number or high..think low??) only focuses on the subject and blurs the background...how much you want the background blurred is up to you...the reverse is when you do a full landscape shot, say, of mountains, and you want everything in focus.. SLR and DSLR cameras have full adjustability, as well as automatic settings...even fairly basic point and shoot digital cameras have the full manual adjustability, but few (with exception of Stig!) ever use it.
A Professional photographer I sat next to on a plane once gave me a great tip ...when you manually set the f stop, and you're taking a portrait, focus the camera on the subject's nose...(good cameras will have a type of dot that shows where you are focusing)..keeps face in focus and blurs everything else
