Re: [Leica] depth of field..depth of focus?

[Martin Howard <mvh@media.mit.edu>]

OK, Henry, don your asbestos underwear, for here goes... ;)

(*WHUMPF* [sound of flamethrower being turned on])

> Depth of focus used as you refer to it is probably of NO CONCERN to 
> anyone who uses conventional cameras that cannot change the position of 
> the film plane. Its built in the camera. Its not changing. 

I seem to remember it changes with aperture and focal length (and possibly
with focus distance too). It may not be of concern to Ted's students at
this stage, it may not be of concern to some of them ever, but it is far
from improbable that one or more of them will become interested enough in
photography to pursue their quest for knowledge further.

> When instructing at the level that Ted was talking about I think "depth 
> of focus" really says it better. An explanation of accepted terminology 
> can happen later.

There is *never* any advantage to lying to students.  Simplifying, yes, but
telling them something that is complete contrary to accepted definitions or
knowledge is, excuse me, just plain stupid.  The *only* thing you will ever
accomplish is confusion at a later date.

Both Depth of Field and Depth of Focus are, at some level, completely
arbitrary constructions.  You might as well call it Amount of Schwabba.  I
fail to see completely why it should be particularly difficult to grasp the
following:

    "Depth of field is the amount of distance between the nearest and
    farthest objects that will appear to be in focus in a photograph.
    When you take a picture, everything within the depth of field is
    going to be rendered acceptably sharp in your photograph."

    (Annoying student at the front raises their hand)

    "Why is it called `depth of field' when it has to do with focus?"

    "Well, `depth of focus' means something else.  For now, just
    worry about depth of field and the index marks on your lens..."

> The detail can be cleared up later. The important part is that the 
> concept is communicated.

Well, in this particular case, with your recommendation, your are muddling
two different concepts.  Details are important, at some level, even for
beginners.  You may not want to give them too much detail in one go, but you
need to give them some detail in order to communicate concepts!  Since that
is the case, you might as well give them the *correct* details.

(*Ffsszzz* [sound of flamethrower being turned off])

There.  Thanks for letting me get that out of my system.  You may now remove
your Nomex underwear ;)


M.

- -- 
Martin Howard                                 (__)                 (__)
Visiting Scholar at MIT Media Lab |           (oo)                 (OO)
fax: +1-617-253-8874              |    /-------\/       ~~~~~~~~~~~~~~~~~~~~
email: mvh@media.mit.edu          |   /|     ||
www: http://mvhoward.i.am/        | ~~~~~~~~~~~~~~
                                  |   Cow in water         Cow in trouble