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An apochromat, or apochromatic lens (apo), is a photographic or other lens that has better correction of chromatic and spherical aberration than the much more common achromat lenses. The prefix apo- comes from the Greek preposition ἀπό- , meaning free from or away from.
An Achromatic telescope uses an achromatic lens to correct for this. An achromatic lens is a compound lenses made with two types of glass with different dispersion. One element, a concave lens made out of Flint glass, has relatively high dispersion, while the other, a convex element made of Crown glass, has a lower dispersion. The crown lens is ...
Chromatic correction of visible and near infrared wavelengths. Horizontal axis shows degree of aberration, 0 is no aberration. Lenses: 1: simple, 2: achromatic doublet, 3: apochromatic and 4: superachromat. In the earliest uses of lenses, chromatic aberration was reduced by increasing the focal length of the lens where possible.
Telescopes can be classified by optical design or mechanical design/construction. Telescopes can also be classified by where they are placed, such as space telescopes . One major determining factor is type of light, or particle being observed including devices referred to as "telescopes" that do not form an image or use optics.
An achromatic doublet brings red and blue light to the same focus, and is the earliest example of an achromatic lens. In an achromatic lens, two wavelengths are brought into the same focus, here red and blue. An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration. Achromatic lenses ...
Often one element is a positive lens made of crown glass and the other is a negative lens made of flint glass. This combination produces a better image than a simple lens. Some Trilobites, which are now extinct, had natural doublet lenses in their eyes. [1] Apochromats can also be made as doublets. Doublets can be air-spaced, cemented, or "oiled".
The telescope is more a discovery of optical craftsmen than an invention of a scientist. [1] [2] The lens and the properties of refracting and reflecting light had been known since antiquity, and theory on how they worked was developed by ancient Greek philosophers, preserved and expanded on in the medieval Islamic world, and had reached a significantly advanced state by the time of the ...
He is particularly credited with the invention of the triple achromatic lens - i.e., apochromatic lens - in 1763, still in wide use today, [3] [4] though known as the Cooke triplet after a much later 1893 patent.