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Re: Pinhole camera



Hi,

Several of us have been discussing the pinhole camera. We
disagreed on using the terms "image" and "focus" in conjuction with
pinhole optics. I claim a pinhole does not focus and thus there is no
image in the sense of an image formed by a system of lenses. My point is
that one should be able to treat the image formed by one optic system as
the object of another system, and that the formation of an image should
not depend of a viewing screen.

I suspect that this is one of those slippery points and I am being
a bit picky, but I looked at a few text and did not find an optical
image defined other than if an object is in plane x and an optical
sytem is at point y with optical characteristics q than the the image is
at z.

Advanced optics text refer to the mapping from the image space to
the object space and imply a one-to-one mapping. A pinhole camera is a
many-point-to-many-point mapping and is either some extreme limiting case
of the acceptable mapping or it just does not form an image.

The best term I have is "optical projection".

Similarly is a shadow an image? How about a diffraction pattern?

An image can be claimed to differ from the pattern of light from a pin hole
in that its properties are different. Images exist at a location, can all
be viewed without a screen (although we do not always do this), and have a
particular size. The pattern from light from a pin hole cannot be viewed
without a screen. The screen can be placed a whole continuum of locations
and the pattern can still be viewed, but it is not fixed in size. So,
while both constitute a one-to-one mapping of sorts there are significant
differences in properties. In fact a case can be made for the claim that
real images can be thought of a the exact superposition of many of the pin
hole patterns.

I do not know of an officially sanctioned term. 'Pin hole patterns' or
'pin hole patterns of light' are what I use in my optics materials.

Dewey

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Dewey I. Dykstra, Jr. Phone: (208)385-3105
Professor of Physics Dept: (208)385-3775
Department of Physics/SN318 Fax: (208)385-4330
Boise State University dykstrad@varney.idbsu.edu
1910 University Drive Boise Highlanders
Boise, ID 83725-1570 novice piper
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