Good First Telescopes
By Chuck Hawks
Omni XLT 102ED. Courtesy of Celestron International.
This article is for the beginning astronomer who wants to see some of the wonders of the universe with his or her own eyes. Although cameras can be adapted to almost all astronomical telescopes, those whose primary interest is taking pictures through a telescope will have to look elsewhere for recommendations.
The major step when taking the plunge into the fascinating world of visual astronomy is buying your first telescope. Keep in mind that your first telescope will almost certainly not be your last telescope. Most observers will own several telescopes as their interests change and their needs mature over the years. What the beginner needs is a simple to use, trouble free telescope that performs up to expectations and provides useful views of the moon, planets and the brighter deep sky objects. A telescope that is easy to set-up gets used; one that is not doesn't.
Start by reading "Telescope Basics" and the "Guide to Beginner, Intermediate, Advanced and Expert Telescopes" on this website. Every hobby has its own lexicon; for definitions of common terms, see "Definitions for the Amateur Astronomer." These articles provide useful information about beginning and intermediate telescopes. These articles provide a foundation of basic information, including common terms associated with amateur telescopes. I am assuming for the purposes of this article that you are familiar with most of this information, so that I do not have to review it here.
The article "I Have a Small Telescope, What Can I See" is directed at owners of 60mm refractors. These are the least useful, but also least expensive, entry level telescopes, provided you get a good one from a specialty telescope manufacturer. (Department store telescopes do not qualify!) This article is intended for the more mature beginner who is willing to start a step above the telescopes specifically intended for beginners by purchasing an intermediate level telescope. This entails more expense, but results in a more rewarding telescope that is useful for a wider range of observing and will serve for a longer time. These telescopes have more light grasp (clear aperture) than 60mm beginner scopes and the more light a telescope can accept, the dimmer the objects it can see.
Most beginner and intermediate telescopes are supplied with mounting systems, including a tripod and head. If not included, a mount will have to be purchased separately. The mounting system is every bit as important as the telescope itself; unfortunately, it is where manufacturers building to a tightly constrained price point tend to compromise. The world's best telescope can be rendered unsatisfactory by an inferior mount.
Whether of the Alt-Azimuth (AZ) or Equatorial (EQ) type, the mounting system must hold the telescope as steady as possible. It must be nearly impervious to vibration and easy to aim with great precision. The latter is usually achieved by means of slow motion controls. Avoid any mount that does not meet this requirement. (This includes Dobsonian mounts!) Good mounting systems are expensive, precision instruments and about 50% of the cost of your new telescope should be in the mount. If it isn't, your new scope is probably under-mounted. When you purchase your first telescope, you are also buying your first mounting system, so give the mount the consideration it deserves.
Alt-azimuth mounts move up and down and side to side, just like most camera tripods. They are the easiest mounts to set-up and the easiest for beginners to understand. A good AZ mount is excellent for "quick look" situations and far superior for occasional terrestrial use. It is an easy mount with which to "star hop." On the other hand, since AZ mounts move the scope in straight lines of elevation and azimuth and the rotation of the earth makes objects in the night sky appear to travel in an arc, the AZ mount must be continuously adjusted in both planes to track an object. This can become a hassle, particularly when viewing at high magnification (and a consequently narrow field of view).
Equatorial mounts are more complicated to set-up and must be at least approximately aligned with the celestial pole (Polaris, or the "North Star" in northern latitudes) to function correctly. This is not difficult, but it is an extra step. Once aligned, an EQ mount moves the telescope through an arc that corresponds to the rotation of the earth. This means that to track a celestial object, the mount need be adjusted in only one direction (called "right ascension" or RA), using only one slow motion control. If the mount incorporates a RA motor, it will track objects without manual adjustment once they are centered in the eyepiece. This is ideal if more than one person will be viewing through the telescope.
Either type of mount can work well. Many advanced astronomers own both types of mounts, using the mount that is most appropriate for the job at hand. For example, I use both a Stellarvue MG AZ mount and a Vixen GPD2 EQ mount with my Stellarvue SV115T telescope. See the "Guide to Alt-Azimuth and German Equatorial Telescope Mounts" for a list of mounting systems categorized by weight capacity. You will also find several individual mounting system reviews on Astronomy and Photography Online.
"Go-to" mounts are motorized, computer controlled mounts (either AZ or EQ type) with a large data base of celestial objects that they can locate for you after the mount is properly aligned. Alignment can be a hassle and, unfortunately, beginners with go-to mounts seldom learn how to navigate the night sky for themselves. This denies them one of the greatest satisfactions from amateur astronomy and for this reason I do not recommend go-to mounts for first telescopes.
The recommendations below are based on my personal experience in the wonderful world of amateur astronomy over the last 20+ years. These are the specific telescopes and accessories I would personally choose for a beginning telescope for myself or recommend to a good friend who was willing to make a medium size investment in this new hobby. Not, you understand, a "cost no object" approach, but not a "tight budget" system, either. I am assuming a basic telescope and mount at a price between $400 and $1500 in 2010 dollars.
After owning a number telescopes, including all three basic types--catadioptric (CAT), reflector and refractor--I have come to prefer refractors or CAT telescopes for beginners and experts alike. Both types have closed optical systems that are easy to maintain and relatively trouble free in use. Newtonian reflectors may provide the most bang for the buck in terms of clear aperture, but they are also more hassle to use and maintain. They require optical alignment every time they are used and require special care because their open mirror systems are susceptible to the entry of dust, dirt, dew and other foreign material. I will, therefore, be recommending CAT and refracting telescopes in this article with a minimum clear aperture of at least 3.15" (80mm).
The use of an extra-low dispersion glass element in the doublet objective of a refractor dramatically reduces chromatic aberration (color fringing), the bugaboo of affordable refractors. All of the refracting telescopes recommended below have two element objectives and all but the least expensive incorporate one ED glass element. I call these "semi-apochromatic" telescopes, although some manufacturers list them as apochromatic. Whatever you call them, visible color fringing of objects in focus should be essentially nonexistent. Triplet ED (true apochromatic) objectives usually offer slightly better performance, but are priced beyond the purview of this article.
Catadioptric telescopes use both mirrors and lenses, typically a front corrector lens of Maksutov or Schmidt design added to the front of a Cassegrain reflector. The result is called a Maksutov-Cassegrain (Mak) or Schmidt-Cassegrain telescope (SCT). These telescopes have a "folded" light path that makes them much shorter than their focal length would indicate. CAT's are usually about 1/3 the overall length of a refractor of the same focal length, making them a standout choice for those with limited storage space. A properly designed and built CAT combines serious light grasp with substantial focal length. CAT's avoid the color fringing of achromatic refractors, but are subject to coma (enlongated star images) at the edge of the field of view. Their corrector lenses reduce, but do not entirely eliminate, this optical aberration.
These are my top choices for sensible entry-level telescopes and mounts, listed in order of approximate online retail price. There are reviews of a number of good intermediate telescopes on Astronomy and Photography Online, including the majority of the specific models recommended here. (For a list that includes a wider range of telescopes for the beginning astronomer, see "Rocky's Telescope List.")
The purchase of a telescope and mounting system is the biggest, but just the first, step in assembling a viable, portable system for amateur astronomy. You will also need, at the minimum, additional 1.25" mounting diameter oculars (eyepieces), moon (ND) filter, star chart, red lens flashlight and other useful accessories. An ocular case and a telescope case will likely prove necessary. A folding table and a portable stool will greatly increase your comfort level in the field. If you want to observe the sun, you will need a full aperture solar filter that covers the front of your telescope. See the articles "A Starter Set of Oculars" and "Telescope Accessories" for additional information.
Cheap oculars are a waste of money. I recommend Celestron, Vixen, Burgess and Tele Vue brand eyepieces, all of which have been reviewed on Astronomy and Photography Online. I prefer Plossl design oculars (specifically Celestron Omni, Vixen NLP and Tele Vue Plossl) in focal lengths from about 25mm up and more expensive designs offering a wider apparent field of view (about 60-degrees) and adequate eye relief (about 16-20mm) in shorter focal lengths. The latter include the Celestron X-Cel and Ultima LX lines, Burgess TMB Planetary, Tele Vue Radian and Vixen NLV.
All of the telescopes listed above will be well served by the addition of a premium 32mm Plossl and an 8-24mm zoom ocular. (I recommend the economical Celestron or upscale Vixen zooms, both of which have been reviewed on Astronomy and Photography Online.) Both Celestron refractors would benefit from the addition of a short focal length ocular of about 7mm. The Stellarvue scopes will require the purchase of a good mirror star diagonal and, in addition to the 32mm Plossl and 8-24mm zoom oculars, at least one short focal length ocular in the 6mm range. For any telescope, keep the magnification of the shortest ocular below about 35 power-per-inch of clear aperture. As time goes by and your experience increases, you will want to add other oculars that specifically address your needs. Clear skies and dark nights!
Copyright 2010, 2012 by Chuck Hawks. All rights reserved.