60 ASTRONOMY • APRIL 2019A proprietary type of
glass, special coatings,
and superb mechanics
make this telescope
one to look through.
by Phil Harrington
T
oday’s state-of-the-art apochro-
matic refractors (APOs) use
two-, three-, or four-element
objective lenses to suppress
optical imperfections that
plague their two-element achromatic breth-
ren. The most common of these optical
imperfections, chromatic aberration and
spherical aberration, are quashed thanks
to sophisticated glass that includes one or
more unusual elements — often f luorite,
SD (special dispersion), or ED (extra-low
dispersion) glass.
The views through these scopes are
second to none and provide magnificent
moonscapes, sharp planetary vistas, pin-
point stars, and deep-sky objects set against
a jet-black background.
Attaining optical perfection comes with
a price, however. Inch for inch of aperture,
APOs are the most expensive class of ama-
teur telescope.Enter Sky-Watcher
Recently, a midpriced class of APOs has
made a big splash in the marketplace. While
still pricey, they strike a balance between
expense and quality. Leading the way is
Sky-Watcher USA’s line of Evostar refrac-
tors. Ranging in aperture from 2 inches
to 5.9 inches, Evostar refractors are built
around two-element objective lenses.
One of those elements is ED glass
designed to help squelch unwanted optical
failings while enhancing image contrast and
sharpness. Although the exact ED glass
used is deemed proprietary information by
the manufacturer, a product specialist told
me that “the glass is a well-known, quality
glass.” Sky-Watcher USA’s MetallicHigh-Transmission Coatings (MHTC) fur-
ther reduce false color, while internal baf-
f ling and a f lat black interior minimize
stray light from infiltrating the optical path.
The f lagship Evostar 150 comes in two
different versions. Both are identical opti-
cally. The only differences are in some of
the mechanics. The Evostar 150 comes with
a Vixen-style dovetail plate and a 2" focuser
with a 1¼" adapter. The Evostar 150DX
includes a dual-speed 3.4-inch rack-and-
pinion focuser with 1¼" and 2" adapters,
rotatable tube rings, a Losmandy D-style
dovetail plate, a 3.75" extension tube, a
Canon DSLR adapter, and dust caps.
Although a finder doesn’t come with either
model, you’ll find a standard shoe-style
base mounted on the tube adjacent to the
focuser. However, you’re on your own for
eyepieces and a suitable mount.Mechanical excellence
This past autumn, I had a chance to put
the Evostar 150DX through its paces to see
whether the designers at Sky-Watcher USA
had achieved their goal. I came away highly
impressed.
The scope’s sturdiness was immediately
apparent as I lifted it out of the heavy-duty,
custom-fitted aluminum carrying case. The
case’s exterior measures 55⅜" long by 15¼"
wide by 11½" high (141 by 39 by 29 centime-
ters), and it has plenty of room inside for
accessories.
The robustness of the case comes at a
price, however: weight. The case alone
weighs twice as much as the telescope. The
Evostar 150DX with the rings and dovetail
plate in place, but without a finder or eye-
piece, weighs 24.8 pounds (11.2 kilograms).When the refractor is nestled in the case,
the pair totals 61.6 pounds (27.9 kg). While
that is manageable by one person — I did it
— it’s best carried by two. There is a single
carrying handle centered on the case, as
well as one at either end. If you will be
transporting the Evostar to a dark-sky site
by yourself, a soft, padded case will be more
practical. Leave the hard case at home for
safe storage.
The tube assembly, with the dew shield
threaded in place and the focuser racked all
the way in, measures 49 inches (124 cm)
long. Tube diameter is 7.1 inches (18 cm),
while the dew shield is 8 inches (20 cm)
across. Inside, three f lat-black light baff les
help suppress unwanted spurious light from
spoiling the view.
The oversized focuser’s drawtube has
3.5 inches (8.9 cm) of back-focus travel. The
focuser is rotatable, and Sky-Watcher USA
marked the drawtube with graduations.
Both features make it easier for photogra-
phers to view through camera viewfinders
and repeat a focuser setting once
established.
The aluminum tube is painted high-
gloss black, as are the focuser and tail stock.
For contrast, the dew shield is gleaming
white while the dovetail base plate has a
green anodization. Together, the colors
blend to create an impressive look.Under the stars
To test the scope, I enlisted the help of my
observing buddy, Rob Guasto. We attached
the scope to his heavy-duty equatorial
mount, and within minutes were ready to
go. The waxing crescent Moon was our first
target. Through a premium-grade eyepiece,WE
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