Page 50 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

INTRODUCTION

TO EYEPIECES

EYEPIECES MAY BE SMALL, BUT THEY PLAY A BIG
ROLE WHEN IT COMES TO ENSURING YOU GET
THE MOST FROM YOUR OBSERVING SESSIONS

The importance of eyepieces took me a long time mount, a fi nder, couple
couple
COATINGS to realise. To say they can make or break you eyepieces and a
as an amateur astronomer may be going a little Barlow lens that doubled
ubled
As light passes through too far, but certainly when you look through a their magnifi cation. Needless
Needless
the lenses in your good eyepiece you realise that what you’ve been to say, I had many, many
many
eyepiece, a little bit
with that
of it is taken away. To observing for all those years could have looked observing sessions with that
ts eyepieces.
minimise this loss of light, much clearer. It all comes down to experience. In fi rst telescope and its eyepieces.
with an eyepiece tray that sat
manufacturers coat the fact, I’m glad I went through the ‘fuzzy faint years’, The mount came with an eyepiece tray that sat
lenses with substances as I call them, because I now appreciate what it between the tripod legs and held the Barlow lens
like magnesium or takes to see the sky properly. – always a useful feature when observing. As all
calcium fl uoride. The The reason my observations were so limited eyepieces are a slightly different length depending
best eyepieces will be
the ones that say they was that I had been bought a small refracting on their power, it was quite easy to feel which was
are ‘fully multi-coated’, telescope for Christmas when I was 10 years which in the dark when I wanted to change the
though ‘multi-coated’ old. It had a metal tripod, a basic altazimuth view. And I took great care of those rather poor
eyepieces are still good.
Try to avoid eyepieces
that are described as
‘fully coated’ or just
‘coated’. One way to
test the coatings is to HOW AN EYEPIECE WORKS
fi x a black cap on the
bottom of your eyepiece
and look down the
barrel in daylight. The
darker the glass looks,
the less light is lost and
the better the eyepiece.

PAUL WHITFIELD X 3, ILLUSTRATIONS BY STEVE MARSH PLÖSSL EYEPIECE BARLOW LENS

This is not so much an eyepiece, but an
Of the 25 or so types of eyepiece around, this
is the one you will mostly hear about as it’s
eyepiece’s friend. A Barlow lens intercepts the
the most common. The internal construction of
light from the telescope before giving it to an
two back-to-back convex and concave lenses,
eyepiece. What this lens does is double or
triple the magnifi cation you would otherwise
and the quality needed for the lens elements,
makes them fairly costly to make and buy.
get from just an eyepiece alone. So, buy your
(around 52°), but eye relief can be a bit short
Barlow effectively double the number of
eyepieces, and therefore powers, you have.
if the lens has a focal length of 12mm or less.
50 skyatnightmagazine.com 2012 Plössls benefi t from a wide fi eld of view eyepieces carefully and let a single well-made