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.
