Point of focus and depth of field work together to create a strong subject point in most photography. Depth of field can be shallow or deep, yet when paired with an altered point of focus, the field appears larger or smaller. Your point of focus is the centre of focus and the depth of field is how much area surrounding that focus point–be it in front or behind–is in focus or is blurred.
Shallower depth of fields are often used to create a “Bokeh” effect. Remember that the depth of field is related to your aperture setting (f-stop) and as such, the lower your number, the lower the depth of field, the more light will be in your photographs. The larger the depth of field, the larger the f-stop, the less light will get in.
Depth of field is also altered by the focal length of the lens that you are using. The longer the lens or the higher the focal length, the shallower the depth of field will be… Even if you are using the same aperture setting!
Observe the following photographs, taken in Gold River at a “Sight Stop.” Each photo is taken with a 50 mm lens at f/3.2 and 1/800 sec with ISO-100:
And just for entertainment purposes, I took this picture while messing around. It gives me a feeling of impending doom, so I thought I would share the vertigo experience: