Re: [ATM] Alternative Petzval Design

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

Richard F.L.R. Snashall wrote:
>
> Here's another design for a 200 mm f/9 refractor (field diameter
> 42 mm or just over 1.25 degrees).
Tweaking this a bit, reducing the aperture a bit further so that
more OTS lenses are available...

Starting with a 500 mm isoconvex and a -350 mm planoconcave lens
(Quantum BXB-250.0-50.8 and PCB-350.0-50.8, respectively) and
adding two identical plano-concave N-F2 lenses (mating with the
OTS isoconvex) and a planoconvex N-BaK4 lens (mating with the OTS
planoconcave),  I ended up with the following 48 mm f/11.7
refractor (563 mm f.l.):

Surf     Radius    Thickness     Glass    Diameter

 STO      258.4          5.5     N-BK7        50.8
   2     -258.4        0.877                  50.8
   3     -258.4            3      N-F2        50.8
   4   Infinity        371.8                  50.8
   5     180.88            5    N-BAK4        50.8
   6   Infinity       61.594                  50.8
   7    -180.88            2     N-BK7        50.8
   8   Infinity            3      N-F2        50.8
   9      258.4      110.775                  50.8
 IMA       2034                           42.14633

The field here ends up at just over four and a quarter degrees
with a visual Strehl of 0.896 to 0.777 over a reasonably flat
field -- perhaps going with some kind of 2" Erfle eyepiece.

My questions:

Does a finder scope with a 2" eyepiece make any sense, and, if so,
is there sufficient space here to comfortably put in a diagonal?


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