Sky and Telescope - January 2018 - 72

ASTRONOMER'S WORKBENCH by Jerry Oltion

A New Criterion
IN OCTOBER AND NOVEMBER of last
year, I wrote about telescope design
many years ago and what's possible
now. This month we see a marriage
of the two in the rebuilding of an old,
8-inch Criterion reﬂector.
The scope dates back to about 1963.
It came to Oregon ATM Larry Myers as
a wedding gift in 2002, but aside from a
few outings and despite relatively good
optics, it mostly sat in storage. Then, as
Larry says, "Fast forward 15 years and
plus one son." Now 10 years old, Logan
has a real propensity for science. So
Larry decided he would ﬁ x up the old
Criterion for his birthday.
"In retrospect," Larry says, "I'm
glad I started many months prior to
his birthday. Taking a closer look at the
mount, I saw that the declination axis

was in need of repair. The bushings were
trashed and the shaft was badly rusted."
Even the castings were shot. So right off
the bat, Larry had to make a whole new
declination assembly. Then a little more
digging showed that the right ascension
axis was just as bad. So what the heck,
he would rebuild the entire mount.
That wasn't as much of a problem for
Larry as it might be for most of us, since
he runs a CNC machine shop. Using
mostly materials already on hand, he
designed and built the mount you see
here. He included optical encoders and
a tracking motor, but decided to make
the scope a Push To rather than a Go To.
Why? "I wanted my son to learn the sky
as opposed to him just pushing buttons."
But it wasn't just the mount in need
of repair. The original pier and legs were

Larry, Logan, and Zupa Myers pose with the beautifully restored 8-inch Criterion.

72

JA N UA RY 2 018 * SK Y & TELESCOPE

pretty ﬂimsy, so Larry replaced those,
too. Eschewing the original aluminum
castings, he designed some hardwood
(cherry) legs, which he laminated crossgrain for strength. One beneﬁt of the
wood besides merely being pretty: The
system dampens vibration much more
quickly than the metal legs did.
Larry used a piece of 6-inch well casing for the pier and had it powder-coated
a dark bronze, which contrasts well with
the brass knobs and other ﬁttings.
Rotating tube rings completed the
mount. That left the OTA, which was,
in Larry's words, "Fairly well made and
well beaten. I re-ﬁberglassed, ﬁlled,
scraped, sanded, messed up, and redid
the whole thing." Eventually he repaired
it to his satisfaction and sent it out
to be Cerakoted, a durable thin-ﬁlm
ceramic coating used in ﬁrearms. It
returned looking brand-new again.
The scope had come with a 1¼-inch
Meade rack and pinion focuser, which
Larry cleaned up and kept, although
he plans to replace it eventually with a
2-inch Crayford. He kept the primary
mirror (which had been replaced with
a Cave optic before the scope was given
to Larry) and the secondary mirror, as
well as the primary cell and secondary
spider assembly. He then added adjustable
weights fore and aft to help with balance.
He replaced the original ﬁnder with
a Telrad and then topped it all off by
adding his old Celestron Comet Catcher
that he had restored several years
earlier. That's a 5.5-inch f/3.6 SchmidtNewtonian - and a pretty hot scope
in its own right. It may be overkill as a
ﬁnder, but you have to admit it looks
awesome perched up there on top of the
ﬁnished Criterion.
First light was, in Larry's words,
"Dismal. I had miscalculated the focal
distance. We could not achieve focus.

L A RRY M Y ERS

Larry Myers raises the bar on rebuilds.
Sky and Telescope - January 2018

Table of Contents for the Digital Edition of Sky and Telescope - January 2018
