Page 34 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

DOUBLE
BUYERS’ GUIDE

There are two kinds of
binoculars: the classic
Porro-prism style used
by astronomers, and the
more compact roof-prism VISION
style, used mainly for
watching wildlife.
If you’re looking to buy
binoculars, fi rst check
you can get a really BINOCULARS ARE AN ESSENTIAL PART
sharp focus with them, OF AN ASTRONOMER’S TOOL KIT
using something that is
really far away. If you
wear glasses, check that Binoculars are a great tool for any observer, and eye ever could.
you can still focus the to begin with there are only a few points worth But before you
binoculars without them.
considering. Having said that, do not let facts and dash outside,
fi gures and overly complicated suggestions get in there are some
the way when the stars are sparkling in a deep dark points to consider.
sky – get out there while the seeing is good! Binoculars can
I bet some of you have binoculars tucked away be heavy, so holding
in a cupboard, used in some past age to watch that them up may give
friendly robin perching photogenically on a nearby both your head and
post box – but what about using them for space? arms some fi ne aches.
You should measure
the exit pupils of your I’ve spoken to many people who have never Add in the magnifi cation
binoculars. These are thought about training their binoculars on the factor, and you’ll fi nd that it’s
the illuminated circles stars. If you don’t have a pair, then ask a friend, a not an easy task trying to hold
you’ll see in each of the relation, a next-door neighbour – some will turn up them still enough for the image
eyepieces when you hold somewhere. The fact that you may not need to pay not to wobble all over the place.
the binoculars away from anything at all in order to help your astronomical Simple things will help in overcoming
your eyes. They should be pursuit is what makes binoculars so good. all of this: rest your arms on a fence or wall
7mm or less in diameter,
and the exit pupils should The overriding factor is doing something, so
also be complete circles. unless the binoculars are truly useless, like the
Next, look through cheap plastic ones that come in a children’s spy kit,
the objective lenses and give them a go. I thoroughly recommend binoculars
eyepieces for purple or for any night-time starry skies adventure, whether
orangey refl ections inside you’re a beginner or are pretty advanced.
the binoculars. These
indicate that the surfaces
of the prisms and lenses BEFORE YOU BEGIN
have been anti-refl ection If you’re out learning the constellations for the
STEVE MARSH, JOHN SANFORD/SCIENCE PHOTO LIBRARY, REV. RONALD ROYER/SCIENCE PHOTO
coated, which is desirable very fi rst time, then a glance through correctly
LIBRARY, TIM HUNTER AND JAMES MCGAHA/GRASSLANDS OBSERVATORY, PAUL WOOTTON
as you won’t lose as much adjusted binoculars will only tempt you to continue
light as it travels through the journey. Some people may suggest that you if there is one nearby, or observe from a deckchair
the instrument.
Prices for a 7x50 should wait until you know your way around the to support your neck. Some binoculars can also be
pair range from £20 to sky without any optical aids before moving on to fi tted to a tripod (with an adaptor), which is another
over £200. We’d sugest equipment. Frankly, this is barking mad: the more solution to the wobbly fi eld of view.
spending at least £50 or you are able to get in the stargazing mix, the better. Now that you’re prepared for action, you can
so, to ensure you’re not What binoculars do, of course, is make things venture out with confi dence. But with the whole
stuck with anything you’ll bigger. With their big lenses, they magnify what fi rmament above you, what should you look at fi rst?
later regret buying.
you’re looking at by grabbing more light than your Here are a few ideas…

FIGURE IT OUT
Binoculars are normally number, the ‘50’, is the A magnifi cation of seven start using a tripod. The
specifi ed by two numbers, size in millimetres of the is really the smallest that bigger the objective lenses,
such 10x50 (‘10 by 50’). objective lenses. These are is any use, and you can the more light your eye
The fi rst number, the ‘10’, the ones at the big end of choose up to 10 before the gets and the fainter the
is the magnifi cation you the binoculars, away from wobble-factor becomes objects you can see, but the
get, while the second your eye. too great and you need to binoculars will be heavier.

34 skyatnightmagazine.com 2012