Sky and Telescope - July 2015 - 74

Gary Seronik
Telescope Workshop

A Minimalist Ultralight
This portable Newtonian is optimized for quick and easy setups.
As i've noted here before, telescope
making can be a bit of a scavenger hunt. Every amateur
telescope maker I know of has a collection of bits and
pieces acquired over the years from friends or at star-party
swap tables. But we also scavenge ideas. Most home-built
scopes are variations on existing designs, but through
little tweaks and additions become something unique.
The 14¾-inch Newtonian reﬂector made by Ottawa,
Ontario ATM Michael Wolfson is a ﬁne example.

MICHAEL WOLFSON (2)

Right: Ottawa,
Ontario ATM
Michael Wolfson's 14¾-inch
f/4.6 Newtonian
reﬂector combines excellent
portability and
performance.
Bottom: Friction in the
altitude axis is
controlled by
turning a hand
knob, which
pulls a pad of
Teﬂon against
the inside surface of one of
the aluminum
side bearings.

July 2015 sky & telescope

"After acquiring many telescopes while searching for
the sweet spot between portability and performance, I
concluded that an ultra-light Dobsonian was the way to
go," Michael says. His goal was to combine the greatest
aperture with the least weight, in a scope that he could
use without standing on a ladder or step stool.
Albert Highe's book, Engineering, Design and Construction of Portable Newtonian Telescopes (WillmannBell), which details building highly portable largeaperture scopes, was one source of inspiration and ideas.
Michael had also seen a single-strut Newtonian at a
star party, which prompted him to build several smaller
versions to gain experience with the design. So when he
acquired a high-quality, 14¾-inch f/4.6 quartz primary
mirror, the broad outlines of his new scope were set.
One feature that Michael put his own spin on was
the scope's bearings. "Instead of counting on Teﬂon and
Formica to provide just the right balance of stiction and
friction," he explains, "I decided to start with bearings
that move as freely as possible, and then increase the
friction in a controlled manner."
His solution uses a 13-inch-diameter Lazy Susan bearing in azimuth, and aluminum semi-circle plates riding
on cam-follower bearings for the altitude. This arrangement is well suited to a motor-drive system Michael plans
to add in the future. But for controllable manual slewing,
some additional friction is required.
To achieve the friction he desired, Michael resorted
to some old-school Dobsonian technology. On the
azimuth axis, he aﬃ xed a 15-inch-diameter circle of
Ebony Star laminate between the ground board and
the lazy Susan bearing, with only the outer inch of the
laminate exposed. With the turn of a knob located inside
the rocker box, a thick pad of Teﬂon gradually presses
against the outer edge of the laminate disk, increasing
friction. For the altitude motion, the aluminum bearing on the focuser side of the scope moves between two
pieces of Teﬂon: one attached directly to the interior
of the rocker box, the other screwed to an adjustable,
spring-loaded aluminum plate. Tightening a knob forces
this second Teﬂon piece against the altitude bearing,
sandwiching it between the two pads - similar to an
automobile disk brake - and introducing extra friction.

Sky and Telescope - July 2015

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