question 4 photographers?

Check out this tutorial.

http://www.cambridgeincolour.com/tutorials/depth-o...

First – Depth-Of-Field (DOF) is the span of distance fore and aft of the point focused upon that is perceived as being in reasonable focus. The DOF zone is not fixed but expands or contracts based on subject distance and camera settings.

1. The span of DOF expands when we focus on a distant subject.

2. The span of DOF contracts when we focus on a nearby subject.

3. The span of DOF expands when the lens aperture is set to a tiny diameter (f/11 – f/16- f/22 etc.)

4. The span of DOF contracts when the lens aperture is set of large diameter (f/1.4 – f/2 – f/4 – f/5.6 etc.

As a rule-of-thumb, the zone of DOF extends 2/3 to the rear and 1/3 back towards the camera as measured from the point focused upon.

5. Short focal length (wide-angle) lenses are perceived to have an expanded DOF zone.

6. Long focal length (telephoto) lenses are perceived to have a shallow DOF

The shallow DOF observed when a long lens (telephoto) is mounted is due to the fact that a long lens magnifies causing the subject to appear nearby. The expanded DOF observed when a short lens (wide-angle) is mounted is due to the fact that the image appears tiny and quite distant. If the images taken with a wide-angle and a telephoto are printed or displayed with different degrees of magnification so the principal subject is the same size on both images, the DOF observed will be identical.

Because depth of field is not just controlled by aperture.

It also depends on the focal length of the lens (wide angle lenses have a deeper depth of field than telephoto lenses) AND the camera to subject distance vs the subject to background distance.

Wow. Second homework question of the morning. Easy. I have the same answer: The idea of homework questions is to get you to study and think. Explain how exactly that getting the answer from some show-boater on Yahoo answers is going to accomplish that educational goal?