Sky & Telescope - August 2024 - 72

S&T Test Report
However, that's where I ran into the
main issue with the 120 APO's mechanics.
The scope arrived with the focuser
seized onto the rear tube section. As
other reviewers have found, it took a
pair of rubber strap wrenches to loosen
the focuser and remove it. I also had the
small M54-to-M48 rear adapters stick
onto the flattener lenses.
The binding of thread-on components
is an issue I've had with most
Sharpstar and Askar telescopes and
astrographs I've tested. Early in the
testing, I applied a thin film of " antiseize "
lubricant to the threads of all the
components, which kept the problem
from recurring.
The only other issue I had was that
in sub-freezing temperatures the camera
rotator became quite stiff. When
I turned it counterclockwise, it would
begin to unthread from the focuser.
Turning it slowly generally worked, but
the grease used in the rotator mechanism
is clearly not made for winter use.
Still, the focuser itself worked well in
both its coarse and fine motions in the
cold, even under load.
Visual Performance
Once the telescope cooled off after
about 40 minutes, the 120 APO passed
my high-magnification star test very
well, with just a trace of spherical aberration.
I saw no sign of astigmatism
even on sub-freezing nights when some
lens cells can pinch optics. In focus,
bright stars looked textbook-perfect,
displaying round Airy disks surrounded
by a first diffraction ring, with a hint
of outer rings coming and going. All
objects snapped into sharp focus. Bright
targets Vega and Jupiter showed no false
color in focus. The close components of
Epsilon Lyrae, the Double-Double, were
cleanly separated by dark sky.
Racking through focus revealed
just a trace of a blue-cyan rim to the
diffraction pattern outside focus and a
A single exposure of the Double Cluster
with the 1.0× Flattener shows the full 2.4° by
1.6° field produced with a full-frame Canon R
camera. The crop of the upper left corner (left)
reveals the negligible level of aberrations typical
of each corner.
Both flatteners are triplet lens designs, with
the 1.0× model (shown above) being the more
substantial of the two in size and weight (at 900
grams or nearly 2 lbs). Each screws onto the
tube with M84 threads and presents M54 and
M48 threads on the camera side, the latter with
a step-down ring that accepts 48-mm filters,
as shown.
pale yellow-magenta rim inside focus.
This is a notch below the color correction
found in the finest triplet apos, but
far better than I was expecting for the
price. I saw some false color only on
high-contrast lunar features, such as
crater rims and mountain peaks along
the terminator. The chromatic aberration
was present only when racking
through focus but was absent in focus.
The 120 APO provides enough aperture
for fine, high-magnification views.
It soon became my scope of choice for
planetary viewing. Jupiter was exceptional
at 210× to 280× on nights of
steady seeing. The scope revealed fleeting
fine texture visible in and around
the Great Red Spot and displayed Galilean-moon
shadows as black ink drops
etched onto the planet's cloudtops.
For great low-power views, removing
the rear tube segment allows a binocular
viewer to reach focus without the
Barlow lens typically required in standard
refractors. Twin Tele Vue 24-mm
Panoptic eyepieces (yielding the widest
field possible in a 1¼-inch eyepiece)
provided 2° panoramic views of star
fields. Nebulae and clusters seemingly
floated in 3D space, and stars
in clusters appeared to be at
different distances. With this
combination, views of the
Double Cluster (NGC 869
and NGC 884) were particularly
outstanding.
A good binocular viewer
provides a superb, if costly,
observing experience. That the
72 AUGUST 2024 * SKY & TELESCOPE
Sky & Telescope - August 2024

Table of Contents for the Digital Edition of Sky & Telescope - August 2024
