Another helpful article ripped from the pages and headlines of the Internet…
DEPTH OF FIELD
by John A.Benigno http://torontophotographysolutions.com/
Depth
of field is the distance range between the nearest and farthest object or
person in a scene that will
appear in acceptable sharp focus. Three
things govern depth of field: lens opening,
Lens focal length and distance at which the lens is focused. Knowing how to increase or decrease depth of field is an important tool for making a photograph something more than a snap shot.
Aperture:
The
larger the lens opening, the less depth of field you get at a given
distance. The area in focus increases as the lens is stopped down.
To check this, note the depth of field scale on your lens barrel.
There
is a series of aperture numbers repeated on both sides of the center index
mark. As you focus, depth of field for any lens opening is indicated
between the f/ number on the left and its corresponding number on the
right. Focus the lens at different distances and watch the depth of field
range increase or decrease according to the distance you set.
Keep
in mind that the indications on the camera depth of field scale are only
approximate, but adequate to guide you while shooting. Depth of field
tables are available for each lens focal length, should you want to study them.
If
your lens barrel does not have depth of field markings, you can stop down the
lens and look through the view finder.
Hyperfocal distance:
Don’t
let the name scare you. All this is is a way to focus using the depth of
field scale on your lens. It varies with focal length, with f-stop and
with the photographer’s need for sharpness, but it is easy to use.
You
simply focus by setting the infinity mark on the focusing scale at the mark for
the f-stop you’re using. The lens is now set at its hyperfocal
distance. As long as you photograph things within that range, you don’t
need to change the focus at all.
Lens focal length:
The
diameter of the lens aperture plus the focal length of the lens are both
determine depth of field. There are complex formulas to calculate depth
of field, but, for our purposes, you should remember this — the shorter the
focal length of a lens, the greater the depth of field it produces at any given
aperture. Here is a comparison to illustrate this for two lenses, each
set at f/8 and focused at seven feet — for a 35mm lens, depth of field runs
between 5 feet and 12 feet, for a 135mm lens, depth of field funs between 6.3
feet and 7.8 feet.
Note:
While it is true that these two lenses produce quite different size images of a
given subject form seven feet, it is also true that if you move back far enough
with a 135mm lens to get the same image the 35mm lens produces at seven feet;
depth of field will be equal.
Focusing distance:
With any lens, the closer you focus to an object, the less
inherent depth of field. In reverse, the farther you focus from lens to
subject, the greater the depth of field.
For
more information about depth of field, and to find depth of field calculators,
as well as hyperfocal distance chart makers, I recommend a visit to johnhendry.com:
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