Sky and Telescope - August 2016 - 60

S&T Test Report

not quite true in practice. The 21- and the 15-mm models
are 2-inch eyepieces and are indeed parfocal with each
other, as were the 10- and 15-mm eyepieces. But the 10and 5-mm eyepieces have 1¼-inch barrels and must be
used in an adapter, which usually places them farther
out in the telescope's focuser. As such, they don't focus
at the same place as the 2-inch eyepieces.

21-mm
This seven-element eyepiece is the most physically
imposing of the MWAs,
and is something of a
handful at 1.68 pounds. In
performance, the 21-mm
was paradoxically the most
and least impressive of
the set. Its huge ﬁeld was
breathtaking, but stars
more than 80% of the way
to the edge of the eyepiece
looked misshapen in my f/5 Dobsonian reﬂector.
Much of this was due to the star-distorting coma
inherent in a short-focal-ratio telescope. When I added a
coma corrector, star appearance improved considerably
across the ﬁeld, but some residual astigmatism in the
eyepiece design meant stars toward the edge were still
not perfect. Unsurprisingly, edge-of-ﬁeld stars looked
better in my f/10 Schmidt-Cassegrain telescope.
I found it important to keep my eye close to the eyepiece's optical axis. Move it to one side and performance
was poorer. I'd get "kidney-beaning," bean-shaped dark
patches in the ﬁeld of view, and also some spurious color
on bright objects. In practice, it was not hard to position
my eye properly and soon became second nature.

S&T: SEAN WALKER (4)

15-mm

While it doesn't oﬀer the
space-spanning views of
the 21-mm, the 1.4-lb.,
15-mm MWA shows a nice
wide swath of sky and its
shorter focal length is less
demanding of the optical
design. Stars at the ﬁeld
edge were respectably
round, both due to coma
being less prominent
because of the 15's lower
astigmatism and its higher magniﬁcation. Eye placement was also less critical than with the 21-mm. Despite
the presence of eight lens elements (which could dim
the view by absorbing some light), objects seemed just as
bright as in other 15-mm eyepieces with fewer lenses.

August 2016 sky & telescope

10-mm
Like the 15-mm, the
10-mm is perhaps a better
balance of ﬁeld size and
optical quality than the
21-mm. Stars were small
and well shaped at the
ﬁeld edge in my SchmidtCassegrain, which made
star clusters look great.
The 10-mm became my
"glob buster," making
short work of smaller
globular star clusters like M92 in Hercules, delivering plenty of tiny stars on a dark background. This one
weighs in at a fairly modest 14.7 ounces, and, like the
15-mm, incorporates eight lens elements.

5-mm
While the 5-mm came up
a little short in the AFOV
ﬁgure, it acquitted itself
well in every other regard.
Stars were better at the
ﬁeld edge than in any of
the other MWAs. Perhaps
the greatest compliment
I can pay this ocular is to
call it a good planetary eyepiece. Saturn was beautiful
in my Dobsonian at 250×,
and its wide ﬁeld meant I didn't have to continually
nudge the scope along to track. This nine-lens-element
eyepiece weighs only 11.8 ounces and handles like a
normal eyepiece.
I thoroughly enjoyed observing with the MWAs, but
beyond the fun, there were a few surprises. The biggest was how well they stacked up to my premium 100°
oculars in use. Stars at the edge of the ﬁeld were not as
good as in premium oculars, but even with the large,
low-power ﬁeld of the 21-mm that rarely bothered me.
I was concentrating on the eyepiece center most of the
time, and only bright "problem" stars on the edge of the
ﬁeld normally caught my attention. Still, when directly
compared with the more expensive eyepieces, the MWAs
presented a slightly softer view overall.
After my testing was done, I just had a ball spacewalking with the Mega Wides. The MWAs are good
performers by any standard, and the fact that they don't
break the bank to deliver means I can't help but be
enthusiastic about them. ✦
S&T Contributing Editor Rod Mollise loves the view through
a quality eyepiece.

Sky and Telescope - August 2016

Table of Contents for the Digital Edition of Sky and Telescope - August 2016