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Old 13-01-2020, 02:59 AM
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Ukastronomer (Jeremy)
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What ??

neo-achromatic telescope

Never heard of it

Yes I know it is a Vixen but what is a neo-achromatic telescope, it is like the disagreement on what a semi-apo is
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Old 13-01-2020, 10:46 AM
Wavytone
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“Neo achromat” is just marketing waffle on Vixens part to con the less-informed that it’s something new when it’s actually quite an old design.

It uses the Petzval design in which a large doublet objective is paired with another smaller doublet midway along the optical path to achieve a well-corrected image. The doublets are designed so that the aberrations of the first are to some extent cancelled by those of the second.

Petzval recognised the net monochromatic aberrations of an optical system are the sum of the contributions from the various elements (when stated correctly mathematically) and through this realised that the aberrations of one element could be designed to cancel those of another. His principle was used to design early photographic lenses, analytically.

In this respect it is not an achromatic doublet since the first doublet is not fully corrected, and the second doublet isn’t either.
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Old 13-01-2020, 06:30 PM
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Ukastronomer (Jeremy)
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Thanks
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Old 13-01-2020, 06:34 PM
Wavytone
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I should add these are quite good and much underrated.
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