Up: Glassmaking
Lens Story: 13 of 28
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ROUGH DISKS OF OPTICAL GLASS
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ultra-microscopes, elsewhere described,
came to the rescue and its possibilities are not yet exhausted.
Stereoscope and Field Glasses
A very skillful instrument for producing the
illusion of relief is the stereoscope. Provided with two views having
the same slight divergence as those received by the two eyes, the
stereoscope fuses them into a perfect semblance of depth and solidity.
The camera which takes these views is provided with two lenses so placed
as to give images exactly similar to those observed with the two eyes.
In the war, stereoscopic views were taken from an airplane at points
separated by 50 to 100 feet, which viewed through an instrument actually
penetrated the enemy camouflage.
Field glasses are as
old as Galileo's telescope. The common form of spyglass, or terrestrial
telescope, differs from the astronomical telescope in having a second
converging lens to erect the image formed by the objective. The erect
image is then magnified by the eyepiece. The opera
glass is identical in its combination of lenses with Galileo's telescope.
Opera glasses are subject to a small field and low magnification, but
give good illumination and can be used in a dull atmosphere.
Binoculars having a wide
field of view, combined with the compactness of the opera glass, have
come into very general use in recent years. The light is made to pass
back and forth between two total reflecting prisms,
DISKS MOUNTED FOR FINE GRINDING
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thereby increasing the actual focal length
of the object glass three times and correspondingly increasing the
magnifying power. The reflections in the two prisms given an erect
image and the greater separation of the object glasses gives better
stereoscopic effect.
Revealing alike the infinitely small and
the infinitely great, the lens has broadened men's minds to embrace a
universe of vast extent. And we have not yet reached the end, for the
dreamer is still with us, and what new realms he may bring to view with
improved methods in optical science, no one dares predict.
SUPPLEMENTARY READING
| THE BOY'S OWN BOOK OF GREAT INVENTIONS, Chapter XIX,
Galileo and the Telescope |
By Floyd L. Darrow |
| STARS AND TELESCOPES |
By David P. Todd |
| SIDELIGHTS ON ASTRONOMY, Chapter on Making and Using a Large Telescope |
By Simon Newcomb |
REPORTS OF SMITHSONIAN INSTITUTION, Vol. 506, 1904,
Construction of Large Telescope Lenses |
| ABOUT LENSES |
Eastman Kodak Company |
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