Sky & Telescope - June 2020 - 31

mirror and its paper donut center mark
using my peep-sight collimator inserted
into the scope's focuser. The primary
mirror is supported in a flotation cell
with three large, easy-to-turn collimation screws. Its secondary mirror
assembly sports a four-vane spider holding a substantial central hub with three
collimating screws for manipulating the
gimble mount on which the secondary
mirror is cemented. Although Explore
Scientific claims the secondary produced a 24% obstruction, the hefty hub
is in fact 2½-inches wide - 31% of the
primary's 8-inch diameter. A blockage
of this size subtly diminishes the visibility of low-contrast planetary detail.

First Light for the FirstLight
I transported the 9½-kg (21-pound)
combo of base plate and rocker box to
my backyard patio. I then lifted the
11-kg OTA using the attached altitude
bearings as handles. Some advice:
Before placing the tube on the rocker
box, ensure the inner lateral guides,
one on each bearing, aren't too tight,
or else the bearings won't fit onto
the rocker base. I loosened the guides
slightly with a 2-mm hex key. Also,
because the guides slide along the
inside of the rocker walls, the slightly
loose fit will result in smoother altitude
motion. (A tighter fit increases friction
in altitude motion, if you prefer.) Be
mindful that the altitude bearings rest
on the rocker. You can rotate the OTA
within adjustable tube rings to bring
the focuser to a comfortable viewing
position and even slide the tube forward and back to ensure best balance
with all your eyepieces. But rotate the
tube carefully or else it will literally
twist off your rocker!
Inserting the supplied 25-mm
"SuperPlೌssl" eyepiece in the focuser
and aiming at a bright star resulted in
an unexpected problem. I couldn't focus
the image, even when the focuser was
racked all the way out. The focal plane
is positioned so far outside the OTA that
a supplied 1½-inch-long "spacer sleeve"
must be threaded onto the focuser
for the use of almost any ocular. The
crucial sleeve is pictured, but not identi-

p The scope's mirror cell features three easily
manageable collimating screws and three
smaller locking screws. Note the textured metal
surface on the altitude bearing (right), which
permits smooth up-and-down motion.

fied, in the pamphlet. In the online
manual, it's erroneously described as an
optional accessory for special situations,
such as "extreme" eyepieces. However,
this extra back focus should allow the
FirstLight to accommodate most any
binoviewer on the market.
After adding the sleeve, I focused the
star and noticed some edge-of-field distortions typical of a fast Newtonian -
nothing serious. Changing to my bestquality 9-mm eyepiece and centering
the star in the 135× field, I was pleased
to behold an Airy disk and diffraction
pattern of reasonable symmetry inside
and outside of focus, with no astigma-

tism evident. Tapping the tube results
in a damp-down time of about three
seconds - not bad.
The telescope's 2-inch rack-andpinion focuser operates smoothly. A
friction screw permits increasing or
decreasing the sensitivity of the focusing motion, and two more knurled
screws at the base of the focuser are for
locking the motion if desired. On my
unit, they didn't lock the motion at all,
though the robust focuser has never
slipped, even under the strain of my
heaviest ocular. In both the 2-inch barrel and the included 1¼-inch adapter,
two knurled screws push against a
compression band to secure eyepieces
without marring your eyepiece barrels
- a nice touch.
For comfortable aiming and tracking, I sat on a stool, one hand on the
front end of the tube and the other
on an altitude wheel. The FirstLight
produces reasonably smooth motion in
both altitude and azimuth. The altitude
bearings, covered by a strip of textured
metal, glide easily atop Teflon pads. A
central bolt at the base of the rocker box
can be tightened or loosened to adjust
tension in azimuth, though loosening
the bolt too much introduces sloppiness.
The only significant stickiness occurred
when I targeted the area around the
zenith - a notorious Dobsonian no-fly
zone. Whenever I stubbornly tracked
an object in the so-called Dobson hole,

p The 2½-inch-wide secondary mirror assembly features a robust central hub that's slightly bigger
than the width (minor axis) of the secondary mirror itself. Its three collimating screws make adjustments easy. The tube's interior is evenly painted flat black throughout.
sk yandtelescope.org * JUNE 2 02 0

31


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Sky & Telescope - June 2020

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

Contents
Sky & Telescope - June 2020 - Cover1
Sky & Telescope - June 2020 - Cover2
Sky & Telescope - June 2020 - 1
Sky & Telescope - June 2020 - Contents
Sky & Telescope - June 2020 - 3
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