I suggest starting with page 138 and 139 in K10D Operating Manual.
I found reading about the
Ultimate Exposure Computer pretty helpful.
This part of the page is specifically about your question, but I suggest reading the whole thing.
It is easier for me to understand DOF, if I can apply some numbers to it. The
On Line Depth of Field Calculator provides information like this:
Camera, film format, or circle of confusion: Pentax K20D,K10DFocal length (mm): 50
Selected f-stop: 2.8
Subject distance: 10 ft
Depth of field Near limit: 9.36 ft
Far limit: 10.7 ft
Total: 1.36 ft
In front of subject: 0.64 ft (47%)
Behind subject: 0.73 ft (53%)
If you would like a more in depth technical look, the
Digital Photography Tutorials at Cambridge in Colour are pretty informative.
Thank you
Russell