Re: Pinhole camera

[Leigh Palmer <palmer@sfu.ca>]

There is a problem with the phenomenon of imaging which is
commonly found with any phenomenon in Nature that shares a
word with a nontechnical counterpart. The apparent lexical
identity often leads to conceptual confusion when the
technical meaning is introduced to the student. I feel that
is the problem with "image" because the word originated in
the nontechnical vocabulary and was subsumed into the
scientific somewhat incompletely. It seems to the student
that there are lots of images that physics ignores. Indeed
the optical images to which physics introduces the student
are often ones with which the student is initially least
familiar.

Roger Haar has raised an interesting point. We should treat
the pinhole camera in our studies of physics. It is easy to
understand, and there is lots of science in it. In my
opinion it does no good at all to tell the student that the
pinhole camera does not form an image. In his frame of
reference that is manifestly untrue; it is not good science.
It is on the same level with the statement made here in North
America that our robins are not "true" robins, or similar
statements which are made about our cedars and Douglas firs.
I have an abundance of all three species in my yard, and one
of them is 38 meters tall. Over the eighteen years I've had
it I've noticed nothing "untrue" about it and have concluded
that there is no useful scientific information contained in
those statements. The definition of "image" is in an entirely
different class: it matters in the teaching of concepts in
physics.

Good definition is always central to understanding. The
example of "species" arose earlier in a biological example.
The term "life" might well have been substututed, for there
is presently no good definition of this fundamental term.
Earlier in scientific history there was a dichotomey with an
absolute religious basis, the distinction between "organic"
and "inorganic" compounds. Wohler shattered that one when he
converted ammonium carbonate (an unquestionably inorganic
compound) into urea, an organic compound. This had
previously been considered a process reserved to the Deity.
Misunderstanding of another definition has been responsible
for killing a number of people comparable to that caused by
the great epidemics of history. It is the definition of "race".

I want to emphasize that the definition of any phenomenon is
fundamental to both description and explanation. It is the
most difficult part in my opinion, and for that reason it is
the most interesting part until it is understood. For those
who do not require understanding the definition is often the
least interesting part. For my part I find gratuitous
denigration the least interesting part of any discussion.

> Hi!
>   I followed the discussion about the "image" given by a pinhole
> camera and found it very interesting. The LEAST INTERESTING part
> was the question about what the proper DEFINITION of "image" should
> be.
>    Regards    Emilio