Sky & Telescope - February 2023 - 71

The optional Carbon
Fiber Tripod includes three
steel spikes to help anchor
the lightweight tripod. The
plastic foot under each leg
is unscrewed and replaced
with a spike.
fiber tripod, which
degrades the accuracy
of the polar alignment,
resulting in fewer
acceptable exposures.
The iPolar system
ily - a testament to the
added precision of the
right-ascension encoder
combined with permanent
periodic correction. Of course,
adding autoguiding resulted in perfectly
round star images with all three setups
even with 5-minute exposures.
Unbalanced Concerns
Eliminating the counterweight bar
and weights is a nice convenience, but
it adds additional considerations that
might not be on a user's radar.
A typical GEM balanced across the RA
axis places the weight of the payload over
the tripod's center. Lacking a counterweight,
the load is unbalanced and offset
toward one side of the mount when the
scope is pointed near the meridian. This
causes flexure in the lightweight carbonconfirmed
this flexure
as the load shifted from
one side of the mount to
the other, seen at right.
The heavier the scope,
the greater the shift. The best solution,
of course, is to add the optional counterweight
system to balance the load.
Heavier telescopes on the unbalanced
HEM27EC introduced another
problem. The off-centered weight made
the entire setup unstable enough that I
was afraid the mount would tip over if
I left it unattended. My 14kg, 11-inch
SCT was dangerously out of balance and
threatened to topple over when pointed
to certain areas in the sky.
The manufacturer provides a partial
solution to this danger in the form
of three steel spikes that replace the
tripod's plastic feet. The spikes are
intended to anchor the tripod firmly
Three combined screenshots from iPolar
reveal some flexure in the tripod under heavier
loads. The central green crosshair indicates
near perfect polar alignment when the telescope
load was oriented on top of the polar
axis in the mount's home position. The red
circle on the right records when the telescope
load was slewed to the mount's extreme west
side. The other red circle shows the shift in
polar alignment when the scope was on the
mount's east side. No shift was detected when
the mount was attached to the author's permanently
mounted observatory pier.
in the ground and ensure your setup
is more stable and secure even when
significantly off balance.
One final issue I discovered when
imaging with this unbalanced system
is that I needed to redo polar alignment
each time I swapped OTAs. No such
flexure occurred when I attached the
mount's head to the permanent pier in
my observatory.
The Bottom Line
After testing the HEM27EC for a few
months, I am very impressed with its
capabilities. Its high-load capacity, accurate
pointing, and outstanding tracking
accuracy are all coveted features -
particularly for travelling astroimagers
who want a quick and accurate setup
capable of working with a wide range
of small telescopes and camera lenses.
Accommodating the limitations of an
unbalanced load is a small price to pay
for the great reduction in equipment
and weight necessary to lug out for each
session. The mount's accuracy and compact
size are particularly attractive for
solar-eclipse photographers looking for
a robust rig for the 2024 event.
Left: The declination axis on the HEM27EC utilizes a standard worm-gear drive, which can be
disengaged when balancing the telescope, as seen here with a 102-mm refractor attached. Right:
The HEM27EC is shown with the author's 8-inch Ritchey-Chrétien telescope. When combined with
the ZWO AZI2600MC Pro camera, the load on the mount reached just over 10 kg, but the combination
tracked very well and produced the image of the Helix Nebula seen on page 69.
¢ Contributing Editor JOHNNY HORNE
is often spoiled by all the amazing technology
in the products he reviews.
sk yand tele scope .o r g * FEBRUARY 2023 71

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