Sky and Telescope - June 2018 - 72

ASTRONOMER'S WORKBENCH by Jerry Oltion

Art Gamble's G-Tracker
Simple. Elegant. Good Enough.

t Art Gamble uses his G-Tracker with one of
his Art Swivel telescopes, featured in the April
2015 issue, p. 70.

72

J U N E 2 018 * SK Y & TELESCOPE

u The G-Tracker
design lends itself to
many different forms;
three variations are
shown here.
uu The plywood version uses a piano hinge
on one end and a metal
plate on the other for
the adjustment screw
to rest on. Either round
the end of the screw
or use an acorn nut (as
seen in the photo at
near right) to produce a
smooth motion.

A RT G A MBLE (3)

WHEN I WAS INTO astrophotography,
I used to spend half an hour or longer
polar-aligning my telescope. Nowadays all I do is visual observing with a
trackball scope, and polar alignment
is a matter of ﬁguring out more or
less where north is and plopping the
mount down sort of aligned with it.
That degree of accuracy is plenty good
enough to keep an object in the ﬁeld of
view for the amount of time I want to
study it.
It would be nice if there were a
simple, elegant way to make alt-azimuth
mounts track with equal facility. Not
necessarily perfect, but good enough.
Art Gamble, whose "Art Swivel"
telescope was featured in our April 2015
issue, has ﬁgured out just such a device,

and it's about as simple as you can get.
It looks a little like a barn-door
tracker: two slabs of wood, a hinge,
and a screw that slowly tilts one of the
wooden slabs upward. In order to put
the hand-knob close at hand while he's
observing, Art added a ﬂexible shaft
made from two grease gun hoses. Since
Art is a retired machinist, he also made
a tracker out of metal. That one comes
in two pieces and works more or less the
same, using the back feet of the moving
part as the hinge. A third design uses a
strap hinge and might be the simplest
of the lot.
To use the G-Tracker, as Art has
dubbed it, you simply put it under the
east leg of your tripod or under the east
foot of your Dobsonian, and turn the
knob attached to the screw. That side
of your tripod or ground board rises
upward, and your scope moves westward. If you're aimed anywhere near
the meridian (the north-south line that
runs directly overhead), your tracking
is pretty much spot-on. The farther you
stray to the east or west, the more your

target takes a diagonal path through the
ﬁeld of view.
When that happens, place your
object a little off-center and let it drift
through center toward the other side
of the ﬁeld while you're tracking. Even
near the horizon, that motion is much
slower than having no tracking at all.
Art reports, "With use, you learn how
to position the object in the ﬁeld to
get the most viewing time. For the vast
majority of the viewable parts of the sky
the tracker works well."
No, it's not perfect, but it greatly
increases the amount of time your
target stays in the ﬁeld of view. As Art
says, "This device is meant to be an aid
to give you more time at the eyepiece;
astrophotographers need not apply."
There are ways to improve its accuracy, though. If you're going to spend
much time in a particular part of the
sky, you can always adjust the mount
so the east leg becomes the northeast
leg, which corrects its aim for objects
in the northeast or southwest; or make
it a southeast leg, which helps in the
northwest or southeast.
You can also raise the north leg of
your tripod or ground board, bringing
it closer to a true polar alignment. For
Sky and Telescope - June 2018

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