Sky and Telescope - June 2017 - 61

Quick Look by Sean Walker

SE A N WA LK ER / S&T

However, the much more affordable
William Optics binoviewer, typical of
most units, did not reach focus, even
when used with a 1¼-inch diagonal. It
still needed its add-on Barlow lens. So
in my judgment the extra back focus
supplied by the focuser wouldn't be
sufﬁcient for most binoviewers without
their accessory Barlow lenses.
At ﬁrst, the focuser exhibited a fair
degree of image shift, but this was
largely eliminated by tightening the two
tiny hex screws on the focuser barrel
that serve to add tension. Even so, a
slight image shift of about 15 arcseconds remained, not serious but a little
annoying when trying to achieve ﬁne
focus while imaging.
More important was what I would
describe as a "general mushiness" in
the ﬁne-focus adjustment. I could turn
the knob and nothing would move at
ﬁrst, then it would grab, even with
the focuser locks off. On occasion it
would outright slip and not move at all,
though not necessarily under a heavy
load. This behavior made it more difﬁcult to nail precise focus. When locked
down, however, the focuser did stay put
with a DSLR camera in place.
The HEX is a nice focuser; it just
isn't top class, at odds with the scope's
premium optics. I would have preferred
to see a small Feather Touch focuser, the
brand supplied with Explore Scientiﬁc's
ﬂagship 152-mm refractor. I would have
also preferred a focuser with more travel,
to reduce the need for swapping among
the suite of extension tubes. Of course,
all of that would add additional weight
and cost to the telescope, partly negating
two of the telescope's top virtues. And
users can always upgrade the focuser to a
third-party model at a later date.
As it is, if the 102-mm's performance
is a gauge, Explore Scientiﬁc's new FCD
100 series delivers superb optical quality
for affordable prices, with the 102-mm
model hitting the sweet spot in cost vs.
aperture vs. portability.

Explore Scientiﬁc's
92° Long Eye Relief
Eyepieces

92° 12- and 17-mm
Long Eye Relief Eyepieces
U.S. Price: $499.99 each
explorescientificusa.com

◗ Since their introduction a decade
ago, extremely wide-field eyepieces
have become a staple among discerning observers. Every time I look through
a big Dobsonian at a star party, chances are the scope is equipped with a
premium ultra-wide-angle ocular with
a 100° apparent field of view or more,
allowing me to drink in the view for a
long period before having to recenter
the view. But these eyepieces come
at a cost, particularly for those who
wear eyeglasses. Often the eye relief
is small, making a tight fit for observers who must wear their glasses when
looking through a telescope.
Explore Scientific's 92° series of long
eye relief eyepieces solves this issue by
providing 20 mm of eye relief with both
the 12- and 17-mm models, allowing
any user to enjoy the entire expansive
field without fussing with their glasses.
I had the opportunity to use both
eyepieces on several large Dobsonians,
as well as my own 12½-inch Newtonian
reflector. Needless to say, the views
are impressive. While not as wide as

What We Like
Superb star images

¢ Contributing Editor ALAN DYER, a
member of The World at Night, authored
the e-book How to Photograph & Process NightScapes and TimeLapses.

What We Didn't Like
Big and heavy

100° models, the difference in apparent
field is slight and only noticeable when
directly comparing the views in the
same telescopes. Stars appear as tight
points of light, with some softening just
before a star reached the field stop.
One particularly memorable view was
with George Normandin's 20-inch Dobsonian during the Stellafane convention
in Vermont last summer. Several of us
lingered on the view of NGC 6520 and
B86, a wonderful pairing of an open
cluster next to a dark nebula. This
dense region of the Milky Way in Sagittarius filled the view with myriad stars,
permitting me to examine the edge
quality of the eyepieces. If you observe
without glasses, I suggest you use the
folding rubber eye guards as a spacer
to position your head to take in the entire field; otherwise, I often experienced
a restricted field when my eye was too
close to the field lens and my head
drifted off-axis.
Perhaps the only drawback to the
92° eyepieces is their weight - the
17-mm tips the scale at 2.56 pounds,
while the 12-mm weighs in at 2.26
pounds. Dobsonian owners might need
some form of counterweight system
when swapping these with smaller,
lighter eyepieces.
The 92° long eye relief eyepieces are
winners for users with or without glasses. I'm looking forward to views through
additional focal lengths in the series.
¢ Equipment Editor SEAN WALKER
enjoys observing with ultra-widefield
oculars, particularly at star parties.
s k y a n d t e l e s c o p e .c o m

* JUNE 2017

61
http://www.explorescientificusa.com http://www.skyandtelescope.com
Sky and Telescope - June 2017

Table of Contents for the Digital Edition of Sky and Telescope - June 2017
