Re: ATMJ #14

["Bill Cook" <atmj1@conceptsnet.com>]

Dear Fellow ATMs:

With Mel's permission, I am posting a list of the articles that appear in
ATM Journal #14, along with four overviews from our new website...so new
that it has yet to be posted.

Starting now, any author having an article published in ATM Journal will
receive a free year's membership or extension.

Kindest Regards,

Bill Cook
Editor / Publisher, Amateur Telescope Making Journal
www.atmjournal.com

**************************
Calculating Mirror Zones (a letter)
By Ken Slater

Figuring a Quartz Schmidt Corrector with Petal Laps (a letter)
By Enrique J. Campitelli

Evolution of a 10x70 Binocular
By Dick Buchroeder

Some Notes on Baffling Newtonians
By Nils Olof Carlin

Improved Test Methods for Elliptical and Spherical TCT Mirrors
By John Francis

A Single-Tube Binocular Newtonian
By Peter Abrahams


The "What Next" Crisis in CCD Imaging
By Richard Berry

If you are like most of us, a year or two after building or buying a CCD
camera, you faced the "what next" crisis. By that point, you had mastered
the camera and the software, figured out how to run a computer under the
stars, and managed to tease reasonable performance from the telescope's
clock drive. You had proven your skills by imaging the Crab, the Lagoon, the
Wild Duck, Hercules, the Trifid, the Dumbbell, the Andromeda Galaxy, the
Triangulum Galaxy, the clusters in Gemini and Auriga, the Orion Nebula, the
Beehive, the Pleiades, the Whirlpool, the Ring, the Black-eye, M81 and M82,
the brighter galaxies in the Virgo Cluster, the Owl, and the Pinwheel: the
Basic 25. Then you asked yourself, "what next?"
Seasoned designer and author Richard Berry explores the next step by
describing three fulfilling programs to keep your CCD juices flowing when
the imaging "blahs" strike...


Design and Construction of a Modern Herschelian
By Gary Frishkorn

The challenge of making a high performance telescope does not end with the
completion of its optics. Effective design and construction of its
mechanical support is also essential in the quest for highest possible
performance. In Part One of this article (ATMJ Issue 13, ed.) I described
the optical design of my 10-inch f/10 Herschelian telescope and the
stressed-mirror polishing techniques used to make its off-axis paraboloidal
primary mirror. The article concludes here in Part Two with a description of
the mount of the telescope. Because the Herschelian is intended for
high-power lunar/planetary observing, its long optical tube assembly
presents a particular challenge to execute. Many aspects of the design
described here can probably be adapted to other long-tube instruments such
as high focal ratio Newtonians.
The bowed-spar truss optical tube is a portable design that
assembles/disassembles quickly, permits collimation adjustments to be made
while at the eyepiece, and reliably maintains collimation between setups...
This thoughtfully detailed article about this Stellafane #1 award-winning
telescope is a gem from both the observer's and builder's points of view. In
addition to construction, the author treats real-time design of baffling for
stray light and thermal problems.


Riverside 1999
By Scott Marsh

Speaking of well-built first telescopes, the showstopper in my opinion was
David Rowe's 11-inch Concentric Schmidt-Cassegrain. The design features a
Schmidt corrector placed at the radius of curvature to cancel spherical
aberration, coma, and astigmatism. The secondary has a radius matching the
primary, giving around a 50 percent obstruction. The design needs no baffle
on the primary mirror, because the supports for the corrector plate and the
large secondary mirror eliminate stray light. ...On the artistic end of the
spectrum, South Californians Jim Hannum and Dave Radesovich co-entered
Newtonians on German equatorial mounts. Both scopes are beautifully
handcrafted from hardwood, using similar techniques. The declination shafts
are lathe-turned, laminated, dark and light woods, giving the impression of
inlay work...
This article by Marsh, a young telescope aficionado, gives the look and feel
of the field at RTMC '99 for those who couldn't make it this time, or want a
retrospective look. Marsh's photography and Loren Busch's digital images of
the entries described complement the article.


A General-Purpose Yolo You Can Build
By Robert Novack

Much has been published about minimizing the size of the secondary mirror
obstruction in Newtonian telescopes. The ultimate answer is to simply
eliminate all obstruction. Tilted component telescopes (TCTs) that do
exactly this have sparked considerable interest over the years. Yet,
extremely long focal lengths, the difficulty of fabricating long-radius
smooth surfaces and the use of more than two mirrors and reflections have
stigmatized most designs. In the mid-1960s Arthur S. Leonard created two
such TCT designs, the Yolo telescope and its three-mirror variant, the
Solano. Leonard named them after counties in northern California where he
lived...

Design Strengths and Weaknesses
The common Schiefspiegler uses two spherical mirror surfaces of the same
radius, with the secondary having a convex curvature. This is simple enough,
the mirrors being tilted at the proper angles to correct for astigmatism.
The setup does not correct for the combined aberrations of two spherical
surfaces, however, and the result is truly objectionable on-axis coma in
systems of moderate focal length. Such a system must be very long indeed,
calling for f/ratios of 24 or greater.
The problem feature of the Yolo is that astigmatism remains uncorrected.
Leonard solved this by using a mounting that mechanically warps the
secondary, pulling on the edge across one diameter, and pushing the edge
along a second diameter perpendicular to the first. This gives the secondary
mirror a slight "potato chip" distortion, a toroidal shape... Jose Sasian
revived the Yolo design in 1988, describing a way to circumvent the bending
of the secondary...

Making the Secondary
I used a black waterproof felt-tip to make a crosshatch pattern on the
mirror and tool, and proceeded to grind with 5-micron alundum. One can
clearly see the high areas grind way first after a few minutes. To keep the
radius constant, one should also alternate between tool-on-top and
mirror-on-top. Go two or three wets beyond good contact just to be on the
safe side. Then proceed to go through your usual process to produce a
well-polished sphere, paying the usual attention to smoothness and quality
of the edge. Remember that any flaws will not go away once the fixture is
loosened. Check the focal length. It should be close to your previous focal
length but it does not have to be exact...
This hands-on article describes the rationale and wherewithal for making a
new breed of computer-optimized Yolo optics. Novack gives a detailed
description of his novel Dakin-style Orthogonal knife-edge tester and the
means of laying out and construction the optical tube assembly.