Creative use of Depth of Field (DoF)

Control of depth-of-field is one of the most creative tools photographers and DSLRs have.  
But what exactly is depth-of-field?
In the most basic terms, it's the distance in front of and beyond the subject that appears to be in focus.


Choose your subject—that rose flower in your garden, for example—and focus on it. Depending on what you decide now, you can make the grass in front of that bush sharp or soft; likewise, the fence behind the bush.
Choose to let the foreground and background go soft and you've effectively isolated your subject and called specific attention to it. Choose to have the foreground and background sharp, and the rose bush becomes an element in the overall scene.
The key to using depth-of-field to isolate or blend your subject is lens aperture. Wide apertures, such as f/2.8 or f/3.5, provide shallow depth-of-field: your subject is sharp, but little else is.

Kishika, My Niece

A Tiny Flower

Narrow apertures, like f/16 or f/22, provide a much greater depth-of-field, so that the territory in front of and behind the subject will be in focus. I haven't shot anything like that yet but, I have shot enough landscapes where you want to get everything in focus.

Sunrise at Liberty International Airport, Newark, NJ

 War Memorial at Washington DC

Simply, the smaller the number, the shallower the depth-of-field; the greater the number, the greater the depth-of-field.