Stardate 10:19:97
Choosing the best telescope for your needs
One decision which every beginning amateur astronomer must make is when he or she decides that it is time to finally get a telescope. It is a decision which should not be taken lightly, for even a modest telescope will cost around $200.
The first question to ask yourself is "What do I want to use this telescope for?".
A telescope meant for casual astronomy could be significantly different then a telescope meant for astro-photography, or terrestrial (earth based) viewing. Just as there is not one car which will be perfect for everyone, there is no single telescope which will satisfy the needs of everyone.
There are three decisions which must be made when selecting a telescope. These are the design of the telescope itself (there are three major choices), the design of the mount (again, three choices), and the outside diameter of the eyepieces (there are three choices here as well, but you will only encounter two of them with instruments of amateur design).
Of course, the most important factor to keep in mind is the quality of the lenses or mirrors. The lenses and mirrors are to a telescope what the engine is to a car. They are the thing which makes everything else work. The best way to ensure that you are buying good quality optics is to buy a telescope made by a top manufacturer such as Meade, Celestron, Orion, or Swift.
The three main designs in telescopes are refractors, reflectors, and mirror/lens systems such as Schmidt/Cassigrains and Makustov/Cassigrains. Refractors contain lenses up in front of the telescope, which bend the light down to where the eyepiece can magnify the image. These were the earliest type of telescope, and they offer instant set up, are low maintenance, and are the design nearly everyone starts in astronomy using. Refractors are, however, expensive to make in large diameters, and thus, are usually only made in small diameters.
Reflectors, on the other hand, are much less expensive to make than refractors; hence, they are generally made in larger diameters than those instruments. When using a reflector, the eyepiece is put on the side of the telescope, near the front of the instrument, easing your ability to view objects high in the sky. They are, however, higher maintenance than refractors, as the two mirrors in reflectors must be kept in near perfect alignment with one another for the best results.
The alignment of these two mirrors is known as collimation. Adjusting the collimation is not difficult or time consuming, but it is a skill which must be learned. Mirror/lens systems are often the best of both worlds, offering low maintenance, decent diameter per dollar, and the ability to easily convert to astro-photography. They do, however, start around $600 due to the fact they are so complex inside, and need several surfaces ground down to very close tolerances.
The three designs in mounts for telescopes include alt/az (or altitude/azimuth), Dobsonian, and equatorial mounts. Both the alt/az and the Dobsonian designs offer instant set up, and ease of use as their primary advantages. They are both simple point and look systems. You move the telescope where you want it, and nudge it along little by little throughout the night. An equatorial mount, on the other hand, must be leveled and aligned with the north star before use.
Once leveled and aligned, however, they have the ability to track objects throughout the night with the turn of only one knob, and you they also have coordinate circles which allow you to dial in the coordinates of a desired object rather than search the night sky for your desired object. The two most popular eyepiece diameters are .96" and 1.25". There is also a 2" system made, but those are, for the most part, professional quality only. If you can afford a 1.25" system, it is well worth the money. The larger the outside diameter of your eyepiece, the larger and easier to view your image will be. You will not see any more of the sky with a 1.25" eyepiece than you will with a .96" system, but it will be projected on a larger piece of glass, making the image easier to view.
One last thing. When looking for a telescope, never let anyone tell you you can get more power out of a telescope than the diameter in inches multiplied by 60. This is the real maximum power of a near perfect instrument under near perfect conditions. You will usually not even be able to go this high. Most high quality viewing is done at much lower powers.
Clear skies, and good viewing.
