Sky & Telescope - March 2023 - 65

ing about the optical performance that
left me feeling that more could be had
from a 127-mm aperture. The scope
easily passed all the typical field tests
that observers do to assess optical quality
- no color halo around bright stars;
identical star images inside and outside
of focus; no hairline color fringes visible
along the Moon's limb; perfect diffraction
images of bright, in-focus stars; and
the clean resolution of tight double stars.
And while on the topic of excellent
performance, that goes for the
SVX127D's optical tube assembly (OTA)
as well. The machining, fit, finish, and
overall construction are all first-rate.
I tested the scope with Stellarvue's
standard dual-speed, 3-inch rack-andpinion
focuser (for an additional $500
an optional Feather Touch focuser is
available). The focuser is attached to the
OTA via a pair of extension rings having
a total length of 80 mm. These can be
removed by those observers planning to
use the scope with a binoviewer.
The whole focuser body rotates so
that the focus knobs can be positioned
in a comfortable horizontal orientation
regardless of where the scope is pointed
when it's on an equatorial mount.
While this is a common feature of highend
refractors, I found it particularly
well done on the SVX127D. The rotational
motion is exceptionally smooth,
and there's enough friction to hold the
focuser's position without using the
The scope's doublet objective
is supplied with detailed
Zygo test data attesting to its
optical qualities and a guarantee
of a Strehl ratio of at least
0.99. See the accompanying
text for an explanation.
thumbscrew lock, even
when there are heavy eyepieces
on a star diagonal.
Inside the OTA there
are four light baffles, and
everything is coated with
an ultra-flat black paint to
suppress internal reflections
from reaching an
eyepiece or camera. I found no sign of
reflections even when observing with
a bright Moon just beyond the field of
view.
Taking It Outside
The bare-bones SVX127D OTA weighs
8.4 kg (18.5 pounds). When you add
tube rings, dovetail bar, diagonal, eyepiece,
and a finder you'll be looking at
closer to 10 kg, which is substantial for
a refractor this size. As such the scope
needs a decent mid-weight mount.
During my tests I used three German
equatorials - the SharpStar Mark III
(reviewed in last January's issue, page
64, and pictured with the Stellarvue
scope), an Astro-Physics Mach 1, and
the iOptron CEM 120 pictured with
this review. All three worked very well,
and while the iOptron would seem
like a bit of overkill I usually had the
SVX127D mounted alongside my heavy,
homemade 8-inch f/8 refractor (built
around a triplet objective made by
Roger Ceragioli). Comparing the views
through both instruments was helpful
for assessing the astronomical seeing
conditions, but not especially meaningful
beyond that given the significant
difference in aperture.
Although I did use the Stellarvue for
some casual deep-sky observing, most
of my testing focused on solar system
objects and binary stars - targets for
which this type of instrument excels. I
could go on at length about individual
observations, but as every experienced
observer knows, the seeing influenced
the views as much as the scope's optical
 Left: The standard dual-speed Stellarvue 3-inch rack-and-pinion focuser includes two dovetail shoes for mounting finders. The author particularly
liked that the whole focuser body could be easily rotated to keep the focus knobs horizontal. Right: The focuser drawtube extends a maximum of 115
millimeters, and the rack-and-pinion drive does not slip even when carrying heavy loads.
sk yand tele scope .o r g * MARCH 2023 65

Sky & Telescope - March 2023

Table of Contents for the Digital Edition of Sky & Telescope - March 2023