Chromatic Aberration
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Index Lens concepts Thick lens concepts | |||||
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Doublet for Chromatic AberrationThe use of a strong positive lens made from a low dispersion glass like crown glass coupled with a weaker high dispersion glass like flint glass can correct the chromatic aberration for two colors, e.g., red and blue. Such doublets are often cemented together (called achromat doublets) and may be used in compound lenses such as the orthoscopic doublet.
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Index Lens concepts "Reference Jenkins & White p 156 ff | ||
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Achromat DoubletsAn achromat doublet does not completely eliminate chromatic aberration, but can eliminate it for two colors, say red and blue. The idea is to use a lens pair with the strongest lens of low dispersion coupled with a weaker one of high dispersion calculated to match the focal lengths for two chosen wavelengths. Cemented doublets of this type are a mainstay of lens design. Another approach to chromatic aberration reduction is to use two positive lenses separated by one half the sum of their wavelengths. Two equal positive lenses are used in eyepieces like the Ramsden eyepiece for correction. Chromatic aberration for three colors can be eliminated with and apochromat triplet.
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Index Lens concepts "Reference Meyer-Arendt Ch 5 | ||
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Apochromatic TripletsBetter correction of chromatic aberration has been achieved than that afforded by the achromat doublets. One could use three lenses to achieve the same focal length for three wavelengths. In practice, so-called apochromatic lenses have been produced in the 4 to 16 mm focal length range for microscope objectives (Pedroti & Pedroti) with the use of fluorite elements.
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Index Lens concepts Reference Pedrotti & Pedrotti | ||
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