Re: [Leica] depth of focus

["Bill Larsen" <ohlen@lightspeed.net>]

Henry Ambrose writes:

|So hows this for a statement using "depth of focus" in a teaching
|situation -
|
|I'd say something like this:
|
|"What I mean by depth of field is maybe simpler to think of as depth of
|focus, the area in your picture that is in focus. This is in a plane that
|is perpendicular to your lens and parallel to the film. "


What wrong with it is that it misdefines depth of focus  --- then you are
going to have to explain why your definition is different than everyone
else's.

For example, Swedlund in his text _Photography_ (which is a commonly used
textbook in beginning and intermediate college photo classes)  defines depth
of focus as:  "the small zone in which the focal plane (film) can be moved
away from a focused lens without incurring a perceptible loss of focus in the
image."  As I recall, one of the touted features of the Leica rangefinder
design is the precise depth of focus.  This was also one of the reasons for
not using a hinged back and using the removable bottom plate instead.

The same text defines depth of field as:  "the zone extending in front of and
behind the point of sharpest focus throughout which focus seems acceptably
sharp and unblurred."  The concept is easy to teach if you have your students
take a picture of a repeating pattern such as fence posts (here we have a lot
of low-traffic railroad lines and I like to use the ties for the
illustration).  The concept of depth of field will become very clear very
quickly.

Regards, Bill (who promised he was going to work and take photographs rather
than LUG it).
ohlen@lightspeed.net