apochromat

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Related to apochromats: apochromatic objective

apochromat

[‚ap·ə′krō·mat]
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However, devotees of fine apochromats also claim that their images have a crystalline clarity and perfection that is beyond price.
From low-cost Asian imports to premium American and European apochromats, the variety of refractors on the market is greater now than ever before.
Some of the scopes listed are plain achromats, others are apochromats, and one is a semi-apochromat.
The best apochromats typically have residuals between 0.010 and 0.015 percent of the focal length, and their images appear free of false color.
While apochromats employ an ever-evolving variety of exotic glass types and specialized lens designs, the basic, two-element achromatic objective has remained virtually unchanged since the mid-1800s.
The rebirth of refractors during the last decade has given me plenty of opportunity to use these instruments, though mostly the new breed of short-focus apochromats made with exotic glass and multielement objectives.
(A Megrez 102-mm f/6.8 refractor is also available for $1,149.) The manufacturer conservatively labels its two Megrez instruments as "semi-apochromatic." The conservatism is laudable--I've seen similar refractors with significantly higher levels of color aberration marketed as "apochromats," salesmanship that stretches the definition of what constitutes a color-free apochromatic refractor.
Up here you won't catch a glint from the lenses of new, exotic apochromats or hear the whine of the latest computer-controlled telescopes, just the quiet musings of amateurs like Johnson silently probing the night sky for hidden treasures.
I began my project by choosing design parameters that matched those typical of commercial apochromats. I settled on a 6-inch f/9 optical system.