OK - I'll try and explain DOF by 2 images. Note that these are just quick 'n' dirty images - a bit of camera shake, dust spots, White Balance (WB) not done, etc. I just grabbed the camera and set it to ISO 3200, natural light. The first shot was at f1.4 (I was using Canon's 50mm f1.4 lens for this test). Note the blurred background. The 2nd shot was taken at f11 and you can see details in the background now (i.e. it's not as blurred anymore). By using f11, rather than f1.4, I was able to gain more DOF. Think of depth of field as the zone of acceptable sharpness both in front, and behind, the subject that you have focused on. Does that make sense?
In my examples, the object of focus was the plastic container. Even though you can't notice it, since nothing was in front of the container, there was a certain amount of space in front of the container that would have been sharp, both at f1.4 and f11. For 1.4, that zone of acceptable sharpness is far less, perhaps a few cm in front and behind the container. At f11, that distance grows to probably around 10cm off the top of my head. If I'd shot at f22, the writing on the Blue boxes in the background would have been readable due to the greater zone of acceptable sharpness that f22 delivers.
Using the zone of sharpness, aka hyperfocal distance, is quite a common tactic when doing landscapes. There is a mathemtical formula for calcualating the correct f stop and focus distance to use etc for maximum sharpness. A few pages of interest:
http://www.cambridgeincolour.com/tut...l-distance.htm
http://www.dofmaster.com/
Hope this helps.
Dave
