In keeping with the universal intent of this thread I thought it might be helpful to post a Technical Note from time to time. It is very obvious there is a vast wealth of knowledge and experience among those that have already contributed to this thread and I encourage everyone to continue to share their knowledge and experience.
Depth of Field
Depth of field is the range of distance within the subject that is acceptably sharp. The depth of field varies depending on camera type, aperture and focusing distance, although print size and viewing distance can influence our perception of it.
I immediately thought of this when I viewed one of Raindog's (Gary Howie) beautiful photos of small town festivals. Aside from being an exquisite photo it is one of the best natural photos that I have seen that demonstrates the concept of Depth of Field.
Notice how the fruit in the foreground is out of focus and gradually becomes clearer as you approach the green peppers. The green peppers are perfectly in focus and as you move further into the background the image gradually gets fuzzy. This clearly demonstrates the range of distance within the subject that is acceptably sharp. Many times depth of field is experienced in photos where the foreground is sharp and the image loses focus as you move further into the background but Gary's photo shows that depth of field is actually a range of focus within the image.
At the other end of the spectrum is another beautiful photo posted by Warren Polidori, Icicles & Berries. In this photo, Warren used an artificial black background so in essence there is no background or depth to the photo and because the camera lens was very close to the subject there is not a foreground to the picture so Depth of Field in this example is a moot point.
For additional information on this topic I have found the link below to be as good as any.
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm