DOF -Depth of FieldMost of the time when we take a photo we expect everything from foreground to background to be in sharp focus. Cameras, however, are not capable of having everything equally in focus and so we make compromises. Our cameras have little boxes superimposed on the viewing screen that we are supposed to put over the most important part or subject of the photo so the camera knows where to put the sharpest focus. Even though everything won't be equally sharp, the type of camera, the type of lens and the aperture settings you select will give you a lot of leeway in the DOF, or the depth of field in your picture.
If you are shooting a landscape with flowers in the foreground, meadows in the middle, and mountains in the background and you want everything in focus you choose a wide angle lens and you choose a small aperture, (which actually is a large number, like f/22). This will give you the sharpest focus possible throughout the picture.
Sometimes, however, you want a limited DOF. For example, when you are doing portraits, you want the person to be in sharp focus, and the background to be a soft blur so that your subject stands out. (Tomorrow I'll post my photo of Chase for his one year portrait that is a good example of this.) To have a shallow DOF you would choose a telephoto lens and a wide aperture (which is a small number, like f/4). This will put objects in front of your subject and behind your subject in a soft blur, while your focus point or subject will be sharp.
When you want to be creative, you can also use DOF to make an interesting picture that is different than what you would normally see, like the examples below:
The photos I took where everyone was in focus seemed too busy. I didn't know where the subject was. When I blurred the background, this photo became more interesting. You can see the boys playing in the background but leaves it to your imagination to decide what they are doing. Chase is clearly the subject, watching his brothers, and you can just imagine him saying, "I want to be bigger so I can play, too."
The next two pictures are from girl's camp. I have lots of photos of the evening programs showing all the girls watching the performers on the stage. I like this photo because it shows the interaction of a few girls, clearly the focus, as they are enjoying the experience.
We were very lucky to have a special guest speaker/singer one night. This is Jenny Phillips, a very popular singer/fireside speaker who has many contemporary LDS CDs for sale. I believe she is under contract with Deseret Book. Anyway, before her part of the program she was sitting in the audience and the girls all sang her song 'Lightkeeper'. I was sitting on the same row so I leaned forward and focused on her so she would be the main subject, while everyone else was softly faded in the background.