[ATM] Dual-Use Refractor

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

A drawing:

    http://users.rcn.com/rflrs/Ptz07-55x.jpg

This is actually the overlay of two telescopes.  The first is
a 290 mm f/7.5 achromat:

    http://users.rcn.com/rflrs/Ptz07-54x.atm
    http://users.rcn.com/rflrs/Ptz07-54x.len
    http://users.rcn.com/rflrs/Ptz07-54x.txt
    http://users.rcn.com/rflrs/Ptz07-54x.zmx

This is basicly similar to a Petzval wit cheap glasses.  The larger
first doublet (N-BK7 and N-F2) is an air-spaced Littrow.  The third
plano-convex N-BK7 lens has a radius that mates with the first surface
of the fourth N-BAK4 lens.  In spite of these constraints, the
system nulls the basics: spherical aberration, coma, astigmatism,
longitudinal color, lateral color, and field curvature).  Two
short-comings are immediately visible:  a) the second doublet has a
considerable air-space (c. 263 mm) and b) the secondary spectrum is
somewhat higher than one would expect from a standard achromat.

The second telescope (also 290 mm f/7.5 with flat field) removes the
last lens of the first design.  That lens is replaced with a five
lens (doublet plus triplet) subaperture color corrector.  Unfortunately,
the corrector is farther up the tube than the lens it replaces.  It
also moves the focal plane out, increasing the instrument length by
about 65 mm; this could present problems with a draw tube design.  The
introduction of lateral color (necessary when the instrument length
is roughly the same) makes the useable field smaller than the original
-- the Visual Strehl is about 0.927 in the center, but drops 2.0
magnitudes from there at the edge of a 26 mm diameter field.

The second design is at:

    http://users.rcn.com/rflrs/Ptz07-55x.atm
    http://users.rcn.com/rflrs/Ptz07-55x.len
    http://users.rcn.com/rflrs/Ptz07-55x.txt
    http://users.rcn.com/rflrs/Ptz07-55x.zmx

Warning to ATMOS and OSLO users:  There are more than 10 surfaces.  In
addition, my versions of ATMOS and OSLO do not have the glass N-SF11.
I inserted that glass as a direct specification.  This could have some
impact on certain analysis features.

Neither of these would "knock your socks off", but the combination may
be of interest.
_______________________________________________
ATM mailing list http://www.atmlist.net/