Sky & Telescope - August 2023 - 69

An optional counterweight kit is
available for $160 that increases the
mount's payload capacity to 18 kg,
though I didn't test it with this option.
A bit more surprising with the RST-135
is that a dovetail saddle to attach your
optical tube assembly is considered an
optional accessory. This is a modular
mount, so you'll need to have or purchase
a dovetail clamp or other means
of connecting your OTA. The head has
many threaded holes to accommodate
a wide variety of options, and Tolga
Astro offers several for purchase on its
website. Fortunately, I had a dovetail
adapter that fit one of its many bolt patterns.
I tested the RST-135 with several
telescopes, including an Astro-Physics
92-mm Stowaway, a Sky-Watcher Esprit
100 refractor, and a Sky-Watcher 180mm
Maksutov-Cassegrain.
Users also need to supply their own
tripod or pier for the RST-135. A tripod
with a wide stance is recommended,
as a telescope with an unbalanced
load may topple over if the tripod
it's attached to doesn't have a large
footprint to accommodate the weight
shifting from one side to another while
slewing to objects around the sky. I was
initially worried about this on my first
outing but soon became more confident,
as none of my loads extended far
enough from the tripod's center of gravity
to cause any problems.
The appearance of the RST-135
Clockwise from top left: The mount includes a soft case, the RST-135 drive head, the Hubo-i
SE hand controller, a hex wrench, the hand controller cable, tripod and PoleMaster adapters, a
2-meter USB 2.0 cable, and two power cables.
is sleek. It's well-machined, with an
anodized finish and solid workmanship
all around. There's no slop or loose
motion in either axis. In fact, because
of the strain-wave gearing (driven by
Swiss-made Maxon DC servo motors),
it's hard to move either axis when the
mount isn't powered up. There are
no clutches or release mechanisms
that permit the axes to swing freely
in order to balance the load. A steady
pressure can move both axes slowly.
When parked with the scope positioned
horizontally, the load will stay in position
when the mount is powered down.
However, if the scope is positioned far
to one side of the RA axis or well out of
tTo make large adjustments when aiming
the RA axis, use the included hex wrench to
loosen the bolt located in the slot below the
large, winged altitude locking knob on the
west side of the mount base.
The north-facing end of the RA axis contains
a guider port, power switch, and three
indicator lights. A USB 2.0 port on the right
side connects the mount to your computer,
while the lower port accepts the Hubo-i SE
hand controller.
balance in the event of a power loss, the
scope will slowly drive down and eventually
collide with the tripod. It's quite a
different story when the power is on - I
couldn't move the scope by hand at all.
The mechanical adjustments on the
mount were smooth and performed well,
even with all my gear mounted up. The
mount arrives with its RA axis aimed
at 90°, so you'll need to move it closer
to your latitude setting. This is done by
loosening a bolt recessed within a slot on
the side of the mount, below the altitude
locking knob. Move the axis until it's
close to your latitude, tighten the bolt
down, then use the large knob on the
south side of the mount to make fine
sk yand tele scope .o r g * AUGUST 2023 69

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Sky & Telescope - August 2023

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