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Re: Pinhole camera

Dewey sez:

Gee, some of us have made the nature and behavior of what one gets from a
pin hole an important feature in materials we use with students for some
time now. We do not tell them that pinholes do not form images (contrary
to what Leigh seems to be implying). Instead we invite the students to
carefully compare properties of real images from lenses and the patterns of
light one gets from pin holes and then we invite the students to decide
whether these are the same entities. For some of use teaching is not
telling.

Leigh sez:
Why not ask them to compare the paterns of light one gets from a lens with
the properties of the image formed by a pinhole camera?

To which Dewey replied:

This is exactly one of the things that is included in what I have my
students do. (Isn't this what my sentence: "Instead we invite the students
to carefully compare properties of real images from lenses and the patterns
of light one gets from pin holes and then we invite the students to decide
whether these are the same entities." means to you. It's what I intended by
that sentence. Sorry if it didn't come out that way.) If you would like a
copy of the materials I use I would be glad to send them.

My point is that you have imposed a theory laden burden upon your students.
You have associated the phrase "real images" with "lenses", and "patterns
of light" with "pin holes". I consider the latter to be what is called "a
leading question" in juris prudence. My version, if properly spelled, is a
question which leads in the other direction by reversing the terminology.
One could now enhance this experience by successive applications of Vaseline
to the lens until its light patterns become less readily interpretable than
the image formed by the pinhole camera.

Are *real* images
like *real* men? They require no other explanation? How do you tell that
you are *observing* a real image?

One of the great triumphs of our species is its mastery of language. More
than any other animals we are capable of communicating sophisticated ideas
to our congeners. For some of us telling is very effective, and it is more
effective by far than "discovery" methods when approaching the more
sophisticated ideas of physics. I consider optical imaging phenomena to be
sufficiently sophisticated that considerable didactic elucidation of their
details is appropriate. Of course some practical work is necessary, but in
my experience students don't learn without both components. This isn't
relativistic quantum mechanics, but it's not easy for the beginner
either.

(Quotation has been reincorporated)

As I turns out I find that "considerable didactic elucidation of their
details" is not necessary. (...making "didactic elucidation" a kind of
oxymoron for me...)

I have failed to communicate irony (my use of language is somewhat less
than perfect)! Please reread with that in mind. I'm a believer in the
indispensibility of old fashioned lecturing as a component in the
instructional delivery system (sarcasm intended*). What appears didactic
to the student who is not "with it" can be revelation to another student.
I happen to be a believer in the importance of the communication of ideas
by means of language.

Leigh

*I sat on a committee of my university in which the rubric "instructional
delivery system" was used frequently. I believe the people who employed it
did not go to the extreme of endowing it with an acronym, but I'm unsure
of that detail at this remove in time. Pain is not cherished and thus,
fortunately, it is remembered imperfectly.

Leigh Hunt Palmer Phone: 604 291 4844
Department of Physics FAX: 604 291 3592
Simon Fraser University Home: 604 299 3731
Burnaby, BC V5A 1S6 email: palmer@sfu.ca
CANADA 122d58m W 49d17m N