Depth of Field

Q: What's depth of field, and how do I use it?

A: Depth of field refers to depth of field of focus. To get a lot of depth of field (i.e., as much in focus as possible), use a small aperture. (Big f-number.) To get very little depth of field, for example to blur the backgorund of a portrait, use a large aperture. (Small f-number.)

For an in-depth (as it were) understanding of depth of field, I would suggest going here:

Cambridge in Colour

But here are some quick practical tips:

• Smaller apertures put more of the image in focus.
• However, the smallest apertures don't give optimal sharpness. Past f/11 or so, diffraction becomes in issue. Most lenses about one-two stops down from wide open.
• For landscape photography, in which you want to optimize both sharpness and depth of field, you should learn about the hyperfocal distance.

• Wide apertures put less of the image in focus. This is often used in portrait photography, where you see a blurred background, foreground, or both.
• A fast prime lens (f/1.4, f/1.8, f/2) lets you get the most shallow DOF. However, if you're shooting portraits, remember that you probably want to have a little more DOF than you can get at f/1.4, especially if you want both eyes infocus. : )
• If you have trouble getting a blurred background because all you have is the kit lens and/or the 55-200, try increasing the distance between the subject and the background.