Archived posting to the Leica Users Group, 1998/06/06

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Subject: Re: [Leica] APO
From: Paul and Paula Butzi <butzi@halcyon.com>
Date: Sat, 06 Jun 1998 09:32:20 -0700

Thanks, Erwin, for this particularly lucid
description.

At 06:20 AM 6/6/98 , Erwin Puts wrote:
>fringing. Normallnses are corrected for two wavelenghts (Fraunhofer lines).
>mostly F (hydrogen: blue) and C (hydrogen: red). For achromatic correction
>the F and C imges are equal and so all wavelenghts between these two are
>also corrected. But there are many wavelenghts still uncorrected. That is
>called the secondary spectrum or 'amount of residual colour'. A lens that
>is apochromatically corrected, has three Fraunhofer lines (C, D and F)
>where aberrations are zero. But there is still some residual colour left.

Do you know, off hand, what the wavelengths for C, D, and F are?

- -Paul