Re: [ATM] Non Achromatic Eyepieces

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Anthony Stillman wrote:

>>...special eyepieces to correct secondary color
>>
>
>The farther the correcting element is from the abberating element, the more
>difficult it is to correct the abberation.
>
>Correcting secondary color half or so way down the light cone is quite
>do-able.  Roger Ceragioli has done some work in this area and reported it.
>Here are links to a few of his postings.  I'm sure I remember a post where
>he described a working telescope that he'd made, but I couldn't find it.
>
>
><http://astro.umsystem.edu/atm/ARCHIVES/FEB00/msg00691.html>
>
><http://astro.umsystem.edu/atm/ARCHIVES/MAR02/msg00539.html>
>
This describes a system that apparently failed; the Corning material
appears to have been about as bad as you can get and still be glass.
Are there any that use a more modern set of glasses?  Although it
uses five lenses instead of three, I wonder about something like:

        R         t           G       d

      9.141      0.25       N-BAF4    3
      2.958         1        N-LF5    3
     -2.958      0.25     N-KZFS11    3
      2.958         1        N-SK2    3
     -2.958      0.25        N-BK7    3
      7.769

(Same primary and primary distance.)
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