aperture

[greygoose]

perhaps i just need to read some material. but i've been wondering:
sometimes when i shoot a photo at a wide aperture (f/ 2.0, f/1.8.) i get a photo where only a small portion of the photo is in focus. i have seen photos where people shoot at f/ 1.2 and if there are two people in the photo both are in focus.

what am i missing here? im sure there is some relation between aperture and distance from camera which i am now trying to find information about so i can catch up.
any further information would be helpful.

[Naturalist]

The more open your aperture is (2.8, 1.8, 1.4) the less DoF you have.

[Atomic79]

There are a few factors left out in your statement that effects apparent DoF besides aperture. Lens Focal Length, Distance of focal point to camera. 18mm lens at f2 focused at a subject 10ft away will have enormously greater DoF than a 200mm f2 focused on the same subject. Something like 5ft - 150ft vs less than an inch for the 200mm.

Check out: On WikiPedia (http://en.wikipedia.org/wiki/Depth_of_field)
or Understand Dof at Cambridgeincolour (http://www.cambridgeincolour.com/tutorials/depth-of-field.htm)

[greygoose]

excellent links atomic.
i will read and reread