Is one of the concepts that makes the difference between a snapshot and a photograph.
(′depth əv ′fēld)
(optics) The range of distances over which a camera gives satisfactory definition, when its lens is in the best focus for a certain specific distance.
In a landscape photograph one expects the entire scene to be sharp, even near objects such as tree branches. In a formal portrait it is more usual for sharp focus to include only the sitter, the background being blurred. Sometimes only the sitter's facial features are in focus: photographers call this effect zone focusing. In all these cases an important factor is what is called depth of field, the distance over which the image appears sharp. It depends on the aperture and focal length of the lens and the distance focused on, and—very important—the criterion chosen for sharpness.
For me, this concept (or technique) was easier to grasp with the 55-200mm Telephoto I have.
The stumpy little limb remnant in the foreground has the focus:
The brick wall now has the focus:
And now the teeny tiny little sproutlet (It IS a word!) has the focus. It is from the middle distance.
And now the slice of cheesy bread has got my attention!
There is some serious Mathematical mumbo-jumbo that goes into calculating this, but I won't bore any of us with that.
Suffice it to say the photos in this post seem to illustrate my understanding of the concept. But more research is clearly called for.
Thinking I may start a photo blog, rather than continuing to bore you with these posts. What do y'all think? You want more? Or should I put these somewhere else and just link to them?