Sky & Telescope - November 2020 - 66

S&T Test Report by Johnny Horne

iOptron's GEM45 Equatorial Mount
This innovative Go To mount can bear a surprisingly heavy load.

GEM45 German
Equatorial Mount
U.S. Price: $2,188 with tripod
and hard case.
ioptron.com

What We Like
Highly accurate slewing
and tracking
Integrated electronic pole ﬁnder
Large payload capacity

What We Don't Like
Assembly requires
tools in the ﬁeld
Hard-to-grip knobs

IOPTRON HAS A REPUTATION of
producing innovative telescope mounts,
from German equatorials to the novel
"CEM" series of center-balanced mounts
that place the telescope saddle over the
tripod's center of gravity, creating more
stability (S&T: Nov. 2018, p. 66).
Among the latest in its line of
traditional German equatorial designs
is the GEM45. Its noteworthy feature
isn't hardware or software related.
It's the number 2.8. That's the advertised ratio of mount weight to payload
capacity. Given that the mount's equatorial head weighs a bit less than 16
pounds (without counterweights), the
2.8 ratio implies it can carry a hefty
45-pound payload.
I tested the GEM45 with four
telescopes of various focal lengths and
weights. All of my tests were done with
the GEM45 mounted on its iOptron
LiteRoc tripod, which features 1¾-inchdiameter steel legs. The tripod stands
29 inches tall and can extend to 48½
inches. Also included in the package is a
hard case with ﬁtted foam for the mount
head, hand control, counterweight shaft,
and the tripod accessory tray.

A Sleek Mount

p iOptron's new GEM45 German equatorial
mount is deceptively small and lightweight for
its stated payload capacity of 45 pounds.

NOVEMBER 2 02 0 * SK Y & TELESCOPE

The GEM45 is an attractive mount with
many CNC-machined parts ﬁnished in
red anodizing that contrasts well with
its black drive housings and removable
stainless-steel declination shaft.
The mount has clutch knobs on
each axis that fully disengage the worm
gears from the main drive gears to
allow quick and easy balancing, and
to prevent damage to the gears during
transportation. Each 110-mm-diameter
worm wheel on the GEM45 is mounted
on large 46-mm-diameter shafts. The
stated periodic error is ±7 arcseconds.
Two additional models of this mount
are available: the GEM45EC ($2,848),

which includes a high-resolution
encoder on its right-ascension axis that
reduces its periodic error to less than
0.25 arcsecond. And as this review was
underway, iOptron announced a version with its newly integrated iGuider
system for $2,498, though it was
unavailable at the time of my tests.

Setup in the Field
Though the GEM45's Go To and tracking were outstanding, the mount's
assembly lacked some conveniences
included in other iOptron mounts.
The tripod's central rod is threaded
on the bottom to permit tightening
of the tripod accessory tray and leg
spreader. Its top is rounded to provide
a central pivot point for the equatorial
head, which is secured to the tripod
with two stainless-steel ﬂathead hex
bolts that require use of an included
4-mm hex wrench. These bolts must be
loosened slightly to permit ﬁne azimuth

q The mount features clutches on each axis
that disengage the worm gears to aid with balance and protect the gears from damage during transit. Also seen here is a USB 2.0 input
jack and iPORT that accepts the GPS dongle or
an optional WiFi adapter.

Sky & Telescope - November 2020

Table of Contents for the Digital Edition of Sky & Telescope - November 2020