[ATM] Maksutov Newtonian Relay

["Jeffrey Kuhn" <jeffrey.kuhn@yale.edu>]

Hello ATMers,

I have been reading the list for a couple of months and this is my first
post. My wife gave me a small 4.5" Newtonian for Christmas and since then, I
have been obsessed with the thought of making a larger instrument. By now, I
have most of the Willman-Bell books on ATM and have read through several.
Since my livelihood involves light microscopy, I am "justifying" my
obsession with telescopes by telling myself that a deeper understanding of
optics will help with my real work.

I hope to have time this spring/summer to start construction on my own scope
and have been thinking of possible designs. Since I am a little
overly-ambitious, I would like to build something slightly more complex than
a simple Newtonian reflector. After reading through Rutten and van
Venrooij's Telescope optics and other sources, I have decided that a
Maksutov Newtonian might be the next step up (3 curves).

With that said, I have also been reading up on Relay Telescopes, including
the Dilworth and Paramythioti-Clave designs, and have been thinking about
incorporating the relay concept into the Mak-Newt design.

As I understand the principle, the relay telescope moves the first focal
plane inside of the optical tube and thus reduces the size of the secondary
mirror (and its obstruction). A second set of lenses then relays this focal
plane outside of the optical tube where it is picked-up by the ocular.

Here is my questions: Is there an existing design that combines a Mak-Newt
telescope with a relay lens?

Here are my initial thoughts:

A normal 200mm F/6 (f=1200mm) Newtonian would need to have the primary focal
plane about 200mm after the 45degree secondary to get the focal plane
outside of the tube. This would place the secondary 1000mm (=1200-200) from
the primary and the secondary would need to be about 33mm+5mm = 38mm wide,
for a 19% obstruction. 

If the relay principle were used, I could place the primary focal plane,
say, 75mm from the secondary. This would place the secondary 1125mm
(=1200-75) from the primary and the secondary would only need to be
12.5mm+5mm = 17.5mm wide, for a 9% obstruction. A relay lens at the edge of
the scope would then re-converge the light onto a second focal plane some
distance away. A small, commercial achromatic lens could be used for the
relay lens but would introduce additional spherical aberrations. However,
the Maksutov corrector at the front of the scope might be made to
overcorrect the spherical aberrations introduced by the relay lens, as well
as support the secondary mirror (no spider).

I haven't worked up an optimized design yet, since I am still evaluating
optics software packages and I don't have access to a nice, expensive,
commercial package.

What are your thoughts on this design?

Take care,
-- Jeff

-------------------------------------------------------
Jeffrey Kuhn, Ph.D.               jeffrey.kuhn@yale.edu
Postdoctoral Fellow                    Yale Univ/MCDBio
Tom Pollard Lab        http://www.yale.edu/pollard_lab/


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