[ATM] 125 mm f/4 Littrow-Lurie-Houghton Refractor

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

A curious design -- 125 mm f/4 design consists of an air-spaced
Littrow doublet and a doublet with Lurie-Houghton geometry
(different glass types, though); hence, the presumed name:

    http://users.rcn.com/rflrs/Ptz06-63x.atm
    http://users.rcn.com/rflrs/Ptz06-63x.len
    http://users.rcn.com/rflrs/Ptz06-63x.txt
    http://users.rcn.com/rflrs/Ptz06-63x.zmx

The Lurie-Houghton lenses are somewhat thin.  However, vignetting
sets in slowly here, so not much would be lost with a somewhat
smaller diameter for that doublet.

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