Now
that we have looked at the 4 basic types of telescopes with
some variations of each, let’s consider these questions and
what I would recommend for a telescope of
choice.
I
call these the
6 "P’s”
1.Price
Reflectors give you
the most light gathering ability for the money. Since we
are, for the most part,
dealing with dim objects this is an important
consideration.
SCT's costs a
little more then reflectors
but usually gives you other advantages such as portability
and tracking.
Refractors usually
are the
most expensive per inch of aperature but yeild very sharp
images and are excellent for
photography.
2. Portabililty
Refracters and SCT’s are the
choice here. Refractors are very portable in 4 inch
aperatures and
smaller.
SCT’s are also
good 8 inches and under.
Reflectors could
also be a good choice for those
6 inches and smaller.
3. Photography
Refractors would be
first choice especially the apochromtics.
SCT’s are also
a good choice.
They both have options for good tracking equipment
available to capture good data for
producing beautiful pictures.
4. Preferences
Deep sky -
(Galaxies, Nebulas, Fain Clusters) -
Newtonian Reflectors are the
choice simply
because of the light gathering power of the larger
aperatures for the money you pay.
Planets, Star Clusters, Moon -
Refractors probably
are the best choice but
SCT’s preform
well.
This
is not to say you can’t use a refractor for galaxies or a
relector for planets but each scope has its
strong points. It all depends on what your favorite objects
might be and how critical your eye
is.
5. Preferred scope?
It’s the one you will use. A scope
isn’t doing anyone any good sitting in the garage or
closet.
So, I hope with this information you will be able to select
the one suited for you and that you
will use it as often as possible and share your enthusiasm
with others.
6. Power
Invariably
when I’m out viewing, especially with my 10 inch dobsonian
people will say, “how much power is that thing?” Without
going into a long explanation I simple say it depends on
the eyepiece you are using. That usually satisfies them but
it really is a little more involved then that.
There
are three distinct types of telescopic
power
1. Light
gathering
2. Resolving
3. Magnifying
I purposely put them in this order because I think Light
Gathering is the most important.
For instance....
Take the Orion Nebula....The nebula will be the same size
thru a 50mm telescope as a 100mm, each using the same
magnification or eyepiece. However, the light gathering
power of the 100mm is 4 times greater than the 50mm. So the
nebula will look 4 times brighter with the 100mm. You can
apply this formula in various ways as you increase your
aperature, or mirror size in other types of scopes.
For the most part astronomical objects are relatively faint
so you can see why light-gathering is important and why I
put it as number one.
What about Resolving? As you
increase the light gathering (or aperture) you can also
increase the power of your scope by changing to different
or more powerful eyepieces. When you increase the power you
begin to resolve (to see) more stars.
That’s where magnification comes in. You
really can’t increase your magnification until you have
enough light gathering power otherwise your image begins to
deteriorate.
Example....
Practical maximum magnification limit is about 2 times per
millimeter of aperature. This means the upper limit for a
60mm refractor is 120 power. Most scopes in discount stores
boast 300 to 400 power. If you push these size scopes to
200 power your images are over amplified and dark. Don’t go
by the pictures on the box.
A scope that is over-powered produces objects that are
dramatically fuzzy and making it impossible to be enjoyed.
Tiny jiggles, wind movements, focusing, “cheap mounts”, may
also add to the ineffectiveness and frustrations of using
the telescope.
For instance... with my little Meade ETX-90 I rarely go
over 100 power. Most of the time it’s 40-70 power. With my
10” dob I rarely go over 300 power but my favorite power
range is 40-200 power.
Just remember that more magnification is not always better.
A clearer smaller image is much better than a larger blurry
one.
I
hope this section on Telescopes was helpful. If you still
have questions please feel free to email me and I will try
to answer them or at least point you in the direction that
will give you the information you need.