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Re: Pinhole camera



"The optical image is the locus of the centers of the waves emerging from
an optical system"

Vasco Ronchi, "Optics. The science of vision, " Dover, 1991.

The Ronchi definition (and Dewey's) are typical of the definitions which
remove the term "image" from the realm of reality. The clear implication
is that the image is localized with mathematical precision in space. I
don't want to put too much of our paper in this discussion, but let me
indicate the, um, lack of depth in such a view of what an image is. Look
in the back of a shiny, nonspherical spoon. Do you see an image? If you
decide that an image exists, you will be hard pressed to find its position.
If you decide an image does not exist you will appreciate the difficulty
which exists in relating physics to what the beginning student considers
to be the real world.

If an image is perceived then the student quite naturally wants to know
why it is there. Physics ought to tell him; that would make it seem more
relevant (excuse my retroBerkeley vocabulary). At present definitions of
image in physics texts ignore many nonconforming images. Arbitrary
attributes of images (real and virtual) are defined which lack generality
and whose only virtue is that they can be tested for and graded easily.
In Nature (which involves perception of the image) there is no difference.
It is not difficult to see why the student comes to suspect the relevance
of physics.

Leigh