Page 38 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

COMPOUND

SCOPES

TELESCOPES COME IN A VAST ARRAY OF SHAPES AND SIZES. HERE WE
LOOK AT THE TWO COMMON VARIETIES OF CATADIOPTRIC SCOPES

Don’t let anyone tell you that choosing a telescope and over several hedges into a fi eld? That could
NAME GAMES is easy. Yes, you could just go out and buy the fi rst have some bearing on the size of the scope.
instrument you see and end up with an absolutely Other things to think about – some are obvious
The odd-sounding names smashing scope. Or, more likely, you could end up when you read them in black and white but can be
for compound telescopes with one that seems too complicated, or big, or any easily overlooked – include cost, how easy it is to
can tell us a lot about number of other negatives. use and what it looks like. Does that deep green
where their designs
came from. It all started That’s not to say the telescope is always at fault. one really look better than the orange
in 1672, when a French There are many people who, on a whim, go out and one? If you’re using it as an ornament
priest called Laurent buy a telescope which may leave the box once; then, in the daytime, does it match the
Cassegrain designed a once the fun and excitement subsides, it ends up wallpaper? Serious decisions indeed.
telescope with two mirrors banished to the loft. The basic telescope forms (that’s
in the arrangement we There are many things you can do to smooth the the refl ectors and refractors) have
recognise today. Then in
1930, Estonian Bernhard process: one of the best is to let those in the know been around for many hundreds of
Schmidt (pictured below) (such as astronomical suppliers or societies) give years, but there are newer designs
added a corrector plate you some hints and tips. But do remember that at that are the choice of many budding
at the front to create the the end of the day, it is going to be your telescope. and experienced astronomers
Schmidt-Cassegrain. How you wish to conduct your brand-new hobby today. These are the compound or
Ho
The Maksutov-ov- may not be the way that experienced fellow has ‘catadioptric’ scopes. I know the name
ma
Cassegrain been conducting his observing for 30 years. Any sounds like something from a hospital
came along be
a
in 1941, advice you’re given must be viewed in relation to ER, but don’t let that daunt you.
w
thanks to the what you want. If you remember, refl ectors use mirrors
refi nements to sort out the light and refractors use
of Russian CONSIDER YOUR SITUATION lenses. Catadioptrics use both
astronomer Things to consider include where you live and
T
Dmitri where you’ll be observing from. Will you just need
w
Maksutov. This Maksutov-Cassegrain is great
to c
to carry the scope into the garden, or into the car for capturing images
HOW THEY Eyepiece Primary Starlight
mirror
SCIENCE PHOTO LIBRARY, PAUL WHITFIELD X3, PAUL WOOTTON X2 These two catadioptric Secondary
WORK
Corrector
plate

scopes are subtly different
mirror
Light entering a catadioptric scope fi rst
encounters a lens that sends the light
down to the primary mirror. The light then
Starlight
bounces back up the tube to a smaller
secondary mirror, or corrector plate, on
the inside of the lens. This then focuses
the light back down, through a hole in the
primary mirror, to the eyepiece.

38 skyatnightmagazine.com 2012 SCHMIDT-CASSEGRAIN