Getting Your Own Telescope
I will not make any attempt to hide my ulterior motive in showing this image
in this introductory page on light and telescopes. This telescope is the Meade
LX200GPS, Schmidt-Cassegrain 14 inch diameter primary mirror telescope, complete
with extra sturdy field tripod, equatorial wedge, 8x50 finderscope, goto computer
program with handheld driver, and a 1.25 inch star diagonal with 26 mm Plossl
eyepiece, SmartDrive, and GPS. All of this for the low price of $4699 plus shipping
and handling. The smaller 12 inch version is on the right of my goal telescope.
Everytime I open the pages of the Sky & Telescope Magazine or Astronomy
Magazine I see the ad for this telescope and drool all over the pages of my
magazine, causing the pages to stick together later on and reduce the pleasure
of my dreaming of owning this scope someday. I continue to hold out hope that
some student of mine will someday fall into a big bucks job and remember their
wonderful Astronomy teacher at Hopkins High School and give me one of these
scopes as a gift of appreciation. That student will probably not be a teacher
or Astronomer because those professions to not pay enough to have that kind
of disposable income. Yet I continue to hope anyway. I am not in any way intending
to promote Meade Instruments, nor have they given me any money. However, if
you ever wanted to purchase a telescope of your own, I would direct you to this
company for your purchase. Here it is again... Meade now is offering a 14 inch
model of the LX200, and for the low, low price of $4695. Imagine the joy you
could bring to my life if you purchase one of these big scopes for me.
But you want to get your own scope and
not one for me. So ... what do you need to know?
First, you need to know a little more about the properties
of telescopes and terms like magnification and light-gathering power. Light-gathering
power refers to the ability of a telescope to collect light. Since the objects
we want to see are far away and dim, we need to build (or purchase) a telescope
that can gather lots of light to produce a nice bright image. Light-gathering
power is proportional to the area of the telescope objective. The area of the
circle is proportional to the square of its diameter, so the larger the objective,
the significantly large the amount of light gathering ability.
Resolving power is the ability of a telescope to separate
two points placed closely together. The high the resolving power, the more able
the telescope is to separate what may look like a single star into the actual
presence of a binary system of two stars. The larger the objective, the greater
the resolving power, and thus the farther out into space you can see things.
Finally, magnifying power is the ability to make a distant
object appear larger. This is perhaps the least important criteria when looking
to buy a telescope. The magnification of a telescope is found by dividing the
focal length of the objective by the focal length of the eyepiece. So, there
you are in a department store, eyeing little telescopes whose advertising claims
"100-power telescope." You have visions in your mind of resolving
the rings of Saturn and seeing the Encke Division in the rings. You pay maybe
$200 and hurry home to look into the sky. Alas, you are disappointed because
you can see Saturn, but it appears so fuzzy that you cannot even tell if those
are rings or ears. High magnification is obtained by small diameter eyepieces.
But small diameter objects have such poor light-gathering ability that the small
eyepiece offers no real help at all. You have just wasted $200!
So you want to buy a better telescope.
Now what do you need to do?
First, go out and get a nice pair of binoculars. Astronomy
is not just about deep space objects, but about the night sky in general. The
more powerful the optics, the more narrow the field of view for your enjoyment.
A pair of binoculars is great for laying on your back and scanning the sky.
Numerous stars of the Milky Way pop into view. You can see the tiny Galilean
moons of Jupiter. You can even find the Andromeda galaxy and some globular clusters.
Then you can point your telescope at something which caught your eye for a closer
The number one rule ... magnification power is not important.
Light-gathering power is. The bigger the lens or mirror, the more light you
can receive from space and the more clearly you can see what you are looking
at. But the increased diameter of the objective makes sky-gazing more focused
and narrow of field. The binoculars offer you the chance to see large areas
of the sky, like constellation borders and star clusters. Binoculars come in
7x35, 10x50, etc. These numbers refer to the eyepiece and objective diameters.
You want binoculars where the second number is big.
Once you have your binoculars, you can step up to a
telescope. The second criteria is telescope type. Simple refracting telescopes
utilize two glass lenses and are the best for viewing planets. However, the
larger lens telescopes are extremely expensive since grinding large glass lenses
is a difficult process. Larger light-gathering telescopes are best found among
the reflecting scopes whose mirrors are more economical and can be pretty big.
The scope in the picture atop this page has a 12 inch mirror, but mirror sizes
range from 4.5 inches to 36 inches. Mirrors larger than that are not for commercial
retail, although Sky & Telescope has been running an ad for years now asking
for a buyer for a 73 inch mirror blank with grinding tools for a bit over $100,000.
Thirdly, the style of the reflecting scope will be up
to you. Simple Dobsonian scopes are nice for finding things in space, but typically
do not have mechanical motors which track the motion of the night sky. Newtonian
scopes are mounted on a tripod and are pretty economical, but the really large
ones require counterweights and the eyepiece is in the front end of the tube,
so ladders are needed to look into them when objects of desire are overhead.
The Schmidt-Cassegrain design is seen in the background image and greatly reduces
the length of the tube, but also costs more that the Newtonian. The Schmidt-Cassegrain
is more portable, which is nice when you live in an area of town where light
pollution makes finding even 1st magnitude stars difficult.
I would strongly getting a scope with a sturdy field
tripod. The flimsy versions you may find at Target will only disappoint. You
may see some objects, but the vibration and difficulty in moving the scope will
frustrate you. Tripods are heavy, so bulk up in the weight room before you get
the bigger scopes.
If you wish to do any photography, you will require
a celestial motor in the scope system to track with the apparent motion of the
sky. For really deep space photographs which require exposure times of an hour
or more, you will need accessories to make fine adjustments while the camera
shutter is open. An alternative to the SLR camera and long exposures is a CCD
camera which mounts in the back of the scope, but now you will need a laptop
to receive the images and process them.
Spend the money and get some nice eyepieces. These are
the tools which increase magnification. Wide-angle eyepieces expand your field
of view and help you search great areas of the sky. Smaller diameter eyepieces
allow you to focus on individual stars or planets. Eyepieces often come with
a set of filters to alter the light and resolve details, or even to reduce light
Some of the newer telescope models come with a computer
inside, preprogrammed to locate stars, nebulae, and galaxies. You set up the
scope, align the instrument to Polaris, turn on the computer, and instruct the
telescope to find an object of interest. The scope will slew to the correct
position in the sky, and voila! there is should be.
Finally, I sincerely believe that you should spend money
liberally. Investing in a cheap scope will always disappoint and it is money
totally wasted. Invest in a fine instrument and you will always be happy. Treating
friends, family, and neighbors to star parties will be your pleasure with a
few more dollars spent up front.
Here are some images of binoculars and telescopes available
from different manufacturers:
Eyepieces and filters
CCD camera by SBIG
Telescope accessories by JMI
Good luck. Now go to the local supermarket or bookstore,
get a copy of Astronomy or Sky & Telescope magazine and find the model which
suits you. If you do buy a scope, drop me a line and tell me what you got. If
you have trouble getting it to work, give me a call. Perhaps someone in your
family would like to purchase a telescope for you, and asks you what you might
want ... hmmm? This sounds like a great plan. So, what are you going to say?
To help you prepare for the possibility that someone
might want to get a telescope for you, please think of 5 good pieces of advice
that you might offer this person (including yourself if you are just going to
splurge on yourself). When you have those 5 pieces of
advice, please share them with my in the form of a response by linking to Telescope
There is a neat little exercise I would like you to
do here for some extra points. Please go to Helping Someone Buy a Telescope.
Otherwise, you have finished the unit on Light and Telescopes. Time
to go forward to Space
Exploration, the Syllabus,
or the Home page.
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