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Starting
Off Right in Astronomy: Part 1
Tom Trusock 10/08
This one's for all the newbies out
there who are interested in looking up at the stars. It's intended
to be a basic introduction into choosing and using a telescope –
y'all more advanced amateurs can just skip it.
There must be something
fundamental
about astronomy. I swear, I don't think I've ever met anyone who
had an aversion to talking about looking at the night sky or thinking
about what's up there. But for some reason, many people just don't
make the jump to observing themselves. I've got some sneaking
suspicions about why that is. I've been worried that many amateurs –
especially some of the more gear oriented ones like you'll see on
line – are unintentionally biased towards the high end of the
spectrum when it comes to talking about gear. That can get a little
– uh – awkward for someone who is looking to ask a basic
question.
And it seems like more and more people
are
asking for advice these days. With that in mind, lets get started.
So ya wanna be an amateur
astronomer? Great! It’s a wonderful hobby – full of rewarding and
relaxing moments – it’s one that you can stick with
through a lifetime.
There's a couple different ways to
approach the hobby. Some folks are gear heads tried and true. They're
easy to recognize. They've always got something new; an
eyepiece, telescope, or some sort of new fangled accessory. Odds
are, they've got one of the more sophisticated setups on the field,
but (and here's the kicker) they may or may not do much observing
with it. These folks like the toys. They like seeing the
differences in performance first hand, and they probably lie
collecting things too. The second type – well, we'll call them
the purists. They care less about the gear and more about the
observing. These are the folks who have a limited amount of gear,
but focus on their observing.
I know a guy – we'll call him
“Bob”. Bob is something of a purist. Bob cares more
about observing the night sky than the tools one uses to do that
with. Bob's out every clear night with his binoculars and his 8”
telescope, and his copy of Nortons (that's falling to pieces). Bob
is in direct contrast to Albert. Albert is the gear head primeval.
Seems like I can't ever talk to Albert without him picking up some
new piece of gear. Last week it was a telescope, yesterday an
eyepiece. It's not uncommon that Al often does not have stuff long
enough to actually observe with it.
Al's a computer guy, and
everything is
goto. If his batteries failed, he'd probably be in a spot of
trouble. Ask him which galaxies he viewed last night and he can
probably rip off a list of 30. He can tell you which telescopes and
eyepieces give the most awe inspiring views on common targets, but
ask him to locate M3, and he'll be lost. Bob on the other hand has
seen more with his 10x50 binoculars than most of us could see with
the Hale. Computers don't dominate his life – in fact, the
only thing he has that uses batteries is his flashlight. And he's
thinking about buying one of those shaker models. If this were travel - Bob, you see, is
more concerned with the view. Al, on the other hand, really likes
the cars.
Which is the right way to do
astronomy? Both! And probably neither too. This is a hobby, when it
comes
down to it, the most important thing is to do it however you enjoy
it. Have fun. If you want to get into the physics of optics –
feel free. If you want to observe a life list of 10,000 objects,
more power to ya. And if you just want to poke out under the stars
with a set of binoculars or a telescope on occasion ala virtual
tourist – even more power to ya.
To get started in this hobby, I
recommend a decent pair of binoculars. We could argue gear for an
eternity, but I'll make it simple and recommend you use what you've
got lying around the house to start. You'll need some charts, and
some ideas what to look at. There's lots of good books and resources
out there. I recommend Steve Coe's What's Up, and my own Small
Wonders articles here on CN. I also recommend a magazine like
Astronomy or Sky and Telescope. Both of these have monthly observing
columns that will present you with a choice of targets.
Binos are a great way to start.
They
really open up the skies, and they are something even the most
accomplished visual observer likes to have on hand for those quick
peeks. If you don't have a set, I recommend you concentrate on
looking at 8x42's (first number is magnification, the second number
is the aperture – how much light they gather) or 10x50's. I
don't really recommend you go any with any smaller aperture (not as
much light gathering) or higher magnification (too hard to hold
steady). I'd say a budget of around $100 - $200 would be plenty –
heck, there are even good deals to be had well below that – but
you'll need to be picky. Later on, I'll give you some tips on how to
check if those binos are worth your money or not, but lets save that
for part II.
At some point you'll probably want
a telescope
– it just seems to be a natural progression. More light
gathering, more flexibility – yeah they're a little less
portable, but every thing's a trade off. So - How do you choose? Well,
first off, lets take a look at the common designs on the market
today.
There’s three main types of
telescopes out there, the refractor, the reflector and the compound
telescope, to help you figure out what’s best for you, I’ll
give a little explanation of each and outline some of the advantages
and disadvantages. Now you vets be a little patient with me, as I
simplify things for the beginners out there. This is going to be
somewhat like high school – yah, it may not be exactly correct
but we’re still teaching the Bohr model – if you know
what I mean…
Refractors -
One for the purist
Refractors come in every size, color and pricepoint.
The refracting telescope is what
most
people think of when they think of a telescope. This design uses
lenses to gather light and is quite popular in the hobby today –
at least in smaller sizes.
Refractors are a low maintenance
design
- you don’t typically have to worry about much with these, just
take them out and use them. They do have some of their own caveats
and pitfalls though – the two biggest being that they need
something to put it on – a mount, and they can – inch for
inch – be the most expensive design on the market.
Most refractors fall into one of
three
categories: Achromatic refractors, apochromatic refractors and ones
that lie somewhere in the middle.
An achromatic refractor is one
that is
corrected for two different wavelengths of light. In practical
terms, this means that you'll see some false color in the image. Bright
targets will be graced with a purple or
yellow/green highlight. In spite of this, achromatic refractors up to
about six inches in size are quite popular with amateurs today,
largely because they are fairly inexpensive, and provide some very very
nice views. Probably the most common type
of achromatic refractor on the market today is the Fraunhoffer
doublet refractor. This utilizes two distinct elements, one made
of flint glass and one made of crown glass to help reduce that
chromatic aberration (false color).
Apochromatic refractors are very
popular with both visual observers and imagers (but a much harder hit
on the pocketbook). Apochromatic
telescopes have better color correction than achromatic telescopes.
Ironically, the definition of achromatic means without color –
since that’s the case, maybe we’d be best off thinking as
apochromatic as “really, really without color, and we mean it
this time!” While there is a technical definition of an
apochromat – based partly on the number of wavelengths it can
bring to a common focus, this is a term we’ll reserve for the
best refractors on the market. Typically, apochromats are made with
two or more elements, typically one made of ED (extra dispersion)
glass. When coupled with the correct mate(s) this results in a color
free system. Top notch apochromatic refractors can easily cost $2,000
and up
just for a 3" telescope alone! And don’t forget, you’ll also
have to provide a mount for these guys.
What then, of the "third" type of
refractor?
Over the past few years,
refractors
have become very popular telescopes, and we’ve seen costs begin
to come down on them – the question you might want to ask at
this point is: Why?
It’s not that the premium
apochromatic refractors have been overpriced - not really. There’s
a lot that goes into a telescope to ensure it’s the best
possible performer it can be. The tolerances are tight – we’re
talking wavelengths of light in terms of tolerances here, and quality
control is a huge part
of the manufacturers cost. There’s also a question of the cost
of the raw materials and the time the manufacturer spends on an item. A
lens that spends more time on a polishing machine and requires
more human input naturally costs more than one that doesn’t. There are
other factors that go into this as well - its simple
economics.
But apochromatic telescopes sell,
and
there are a lot of companies that are bringing to market decent
quality telescopes at a fraction of the price of some really high end
gear. So what do you sacrifice with these? Typically color
correction and corrections for some types of aberrations (the image
isn't as sharp and pinpointy). You can
also count on lower QC as well. They also tend to use less
expensive materials – some of the less exotic glasses are quite
a bit cheaper and while they offer decent performance it’s not
quite up to the level of their more expensive brethren. You'll
also find that there most likely isn't the same amount of attention
paid to selecting the glass to make sure of it's quality, and there's
typically less time spent figuring and polishing the lenses as
well. You'll also find that the mechanicals (tube, focuser, etc)
these manufacturers offer is a step below the truly top notch companies.
You'll find that the third type is
symbolized by the
"inexpensive" 80-102+mm apochromat – many of these scopes don’t
quite offer the color correction their more expensive brethren do –
in fact by strict definitions, many would probably not even qualify as
apos. And yet
these guys have a great following – largely because their price
makes them affordable to a wide section of the marketplace and because
they really can deliver some fantastic views.
The Newtonian
Reflector – Go Deep!
Probably the most common telescope on
the market today is the Newtonian reflector on a Dobsonian mount.
Without question, these guys offer the best “bang for the
buck”. There's a saying out there – Aperture rules. And
all things being equal (figure, cool down, etc) that's 100% correct.
And this is where aperture walks
in.
Good Newtonian reflectors gathers
light
using a parabolic mirror. (Run
away from any that offer spherical mirrors.) Unlike most
refractors, they need to be collimated. In this sense, it's
maybe a little more fiddly than a refractor, but the process is still
pretty
easy to figure out and the gain in the views is really worthwhile.
Newtonians on Dobsonian mounts
(we'll
just call them dobs from here on out) have a few disadvantages – as
I've already mentioned, they do require collimation; that is their
optics do need to be
aligned. The mirrors are what's called “First Surface”
mirrors. That means the reflective material is on the front of the
glass, not the back of the glass. The upshot is that it's not
protected by the glass. It will decay and in a few years (anywhere
from 10-20) you'll probably have to start thinking about getting that
mirror recoated. Because of the nature of the parabolic curve used
to reflect light, newts do tend to show an aberration called coma as
you move away from the center of the field (we say as you move
"off-axis"). Coma is an
optical aberration that turns stars into comets. The good news most
folks
typically don't notice it in these common beginner scopes, and if you
go beyond them, there are solutions out there to drastically reduce
if not eliminate coma in the system.
Truss dobsonians break down into smaller packages
than their solid tube counterparts. This helps
with transportation.
And one more drawback all that aperture can be
heavy to carry if you've got to constantly lug it up and down the
stairs every time you want to view.
On the upside, if you want to see
detail in deep sky objects – this is what you want.
Newt's are for the visual
observers, a
club of which I count myself a member. Unfortunately, I sometimes
have the distinct feeling that we may be something of a dying breed -
but that's a topic for another article.
The
Compound Telescope – One for the Gadget Lovers
And then finally, there's this
third
category – these guys are a mixture of the previous two in that
they use both lenses and mirrors to gather light. There are a
number of variants here, all with their various pluses and minuses.
Among the more popular, we've got Mak-Newt's, Schmidt-Newts,
Mak-Casses, Schmidt Casses and Meade's new(er) ACF.
 Meade offers a line of Schmidt-Newt's
that provide the observer with a very wide,
well corrected field.
The most popular
is probably the Schmidt Cass or SCT. Available in apertures from 5”
to 16”, I won't presume to step on Uncle Rod's toes (he's
written the book on them – seriously), but I'd encourage you
to drop him a line and ask if you've got specific questions on the
design. All in all, the SCT is an amazingly
versatile design. It's fairly small, yet packs a lot of aperture for
the size. The eyepiece is nearly always in a fairly convenient
location, and they pack a pretty good bang for the buck –
especially if you purchase off the used market. If you're a gadget
lover, you'll probably want to take a long hard look at the SCT -
there's tons of accessories for these scopes.
On the downside, the common mass
produced SCT can be something of an exercise in averages, and they
can be a bit fiddly as per collimation – and you DO need to
collimate these guys. But if you take some time to learn about the
design, and how to optimize it, you can get some amazing views.
While I'd say (in general)
refractors
lean towards the imaging crowd and reflectors towards the visual –
SCT's really go both ways. They tend to a jack of all trades.
Unfortunately, there's a second half to that quote, but everything's a
trade off....
Up Next,
Part 2 – Choosing your
first bits of gear
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