Sky & Telescope - August 2021 - 61

ALL IMAGES COURTESY OF THE AUTHOR
(2.8 inches) lenses and high magnifi -
cation. Not so! While big, high-powered
binoculars do have their place,
they lack many of the advantages I
just listed. My advice is to avoid the
temptation of magnifi cations greater
than 12×. Simply put, more power
doesn't always equal a better view.
Out of all the combinations of
42 mm
APERTURE TRIO The bigger the front
lenses, the brighter the images, but the
heavier the binoculars. If you're looking for
all-purpose binos, a lightweight 42 mm is
a fi ne choice. While 56-mm binoculars are
great for astronomy, they can be heavier
and harder to hold steady.
50 mm
power and aperture on offer, binoculars
with lenses 42 mm to 50 mm in
diameter and magnifi cations from
7× to 10× yield the best combination
of light-gathering and resolution
without sacrifi cing the wide fi elds of
view and hand-held convenience that make binoculars such
a joy to use. These are the models I reach for most often for a
night of stargazing.
While 42-mm binoculars are ideal for all-purpose use,
56 mm
when shopping for binoculars primarily for astronomy,
consider a 50-mm model. The extra aperture will gather
about 40% more light, allowing you to see objects nearly
½ magnitude fainter.
Most 50-mm binoculars tip the scales at 800 to 1,000
grams (28 to 35 ounces), which makes them about 100 to
300 grams heavier than 42-mm binoculars. However, unlike
daytime users such as birders, we astronomers don't carry
our binoculars around for hours at a time, so a bit more
weight is a tolerable trade-off for brighter images. Even so,
any model weighing much more than 1,000 grams can be
diffi cult to hold up to the sky for
more than a quick glance. In general,
binoculars with 50-mm lenses
provide a good balance of aperture
versus weight. And that's why I'll
focus my attention on 50-mm binoculars
in this survey.
So what about magnifi cation?
Among binocular astronomy enthusiasts, the hot debate
used to be between choosing 7×50s or 10×50s. The 10× camp
argued that the higher magnifi cation resolved detail better,
while the 7× camp countered that the extra magnifi cation
made 10× binoculars harder to hold steady.
Today the debate is effectively over. Buy the 10×50s. The
reason is simple - there just aren't many 7×50s being made
anymore. With the exception of heavy and costly binoculars
for marine use (from companies such as Fujinon and
Steiner), the few 7×50s left are budget models ($100 and less)
with narrow fi elds of view and performance that's inferior to
most 10×50s.
If you have shaky hands and prefer lower magnifi cation,
consider 8×42 roof-prism binoculars of the best quality you
can afford. (I'll say more about the two main prism types
BINOCULAR ENSEMBLE For stargazing, a pair of 10×50s is arguably the best choice. The designation indicates a magnifi cation of 10× and front
lenses that are 50 mm in diameter. It's a popular size with many different models to pick from.
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