In class today, I said that terrestial telescopes have the advantages of
being more compact than astronomical (refracting) telescopes and producing
erect images. So somebody put up their hand and asked why *all* refracting
telescopes, and microscopes for that matter, aren't made with a diverging
rather than a converging eyepiece?
Frankly I'm not sure of the answer. I said that I supposed that convex
lenses are cheaper than concave lenses. But are there other reasons - eg.
Would a diverging eyepiece have to be larger in diameter than a converging
eyepiece? (I would think not.) Perhaps the fact that real telescopes and
microscopes are more complicated than the simple two-lens textbook models
(in order to minimize aberrations) favors convex lenses? (Is there such a
thing as aspheric concave lenses? If not, why not?)
By the way, are reflecting telescopes ever constructed to be erect (by
using a diverging eyepiece)? And is there such a thing as a reflecting
microscope?
Finally, in lab we measure experimentally the magnification of a telescope
by holding up a ruler at arm's length and looking through the telescope
with the other eye. I've tried to do similar things with a microscope, but
it's hard to do, as are alternatives like trying to draw the size of the
image on the eyepiece. Is there a workable way to experimentally estimate
the magnification of an approximately 2X microscope (suitable for a
low-cost introductory lab)?
Dr. Carl E. Mungan, Assistant Professor http://www.uwf.edu/~cmungan/
Dept. of Physics, University of West Florida, Pensacola, FL 32514-5751
office: 850-474-2645 (secretary -2267, FAX -3323) email: cmungan@uwf.edu