Re: [ATM] Alternative Petzval Design

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

Richard F.L.R. Snashall wrote:

>This is a 290 mm f/7.5 Petzval design. Glass selection was based
>on "cheap". In spite of that, the Visual Strehl is about 0.555.
>

By leaving a bit of C-F lateral color difference (i.e. the C line does
not precisely match the F line w.r.t. lateral color), and shifting the
one glass -- here's a design that can have the second doublet cemented
or oiled; the expansion difference is small.  While an additional
thickness of the first doublet makes this not quite a cheap, the glass
is more familiar and there are two less air-glass surfaces to worry
about.

    http://users.rcn.com/rflrs/Ptz03-46x.atm
    http://users.rcn.com/rflrs/Ptz03-46x.len
    http://users.rcn.com/rflrs/Ptz03-46x.txt
    http://users.rcn.com/rflrs/Ptz03-46x.zmx

It also has somewhat larger zonal error, but not huge -- it is still
about lambda/90 P-V for the e line at its central focus.

I also reduced the aperture 2 mm; the total length of this one is under
2.5 m.
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