Telescope Buying Advice
Advice for First Time Telescope BuyersAre you thinking of buying your first telescope? The most important step in deciding which type of telescope to buy is to first understand what it will be used for. We suggest that you stop to ask the following questions about your expectations of this first telescope before proceeding further:
The answers to these questions will start to narrow your choices considerably. A Few Simple RecommendationsHere are three general guidelines for choosing your first telescope. Images and a brief description of the different types of telescope are found further down on this page. If your interests are limited to the moon and planets, then many small telescopes will meet your needs. As mentioned earlier, a Refractor with 90mm of aperture is all you will ever need. Small Maksutov-Cassegrains will also get the job done, as will Newtonian Reflectors of up to 130mm aperture. In many cases you will need an additional eyepiece to achieve the magnification needed to get a good look at the planets. Look carefully at the specifications for the telescope to see if it includes an eyepiece that will deliver at least 100x magnification, although 150-180x is usually ideal. If you don't see that you should budget an additional $50-70 for another eyepiece or a Barlow lens. If your interests extend beyond the solar systems to deep space objects, then consider six inches of aperture the bare minimum. Larger is better, provided it is within your budget. Dobsonian telescopes are a popular and cost effective choice for this application. Expect to pay $300 for a basic manually operated six inch Dobsonian. If you don't have confidence in finding targets on your own, or if you are observing from light polluted urban skies, we highly recommend a "Go To" telescope that will locate and track objects for you. Without the aid of this technology you will be hunting targets based upon their proximity to a star or stars that are visible to the naked eye. We call this "star hopping." People living in heavily light poluted urban or suburban environments will find this difficult with very few visible stars to act as guide posts. While any telescope type may be combined with a go to mount, Schmidt-Cassegrains are the most common. Larger go to telescopes suitable for observing deep space objects start at about $800. Telescope Optical DesignsBelow is a summary of the different types of telescopes found on this website, including their strengths an weaknesses. We also highly recommend the Advice for Beginners written by Ed Ting, amateur astronomer and contributing editor for Sky and Telescope magazine. And by all means feel free to give us a call for some friendly and honest advice. RefractorsRefractors or refracting telescopes are a design that use only lenses to focus the light; every other type of telescope relies on one or more mirrors to do that job. The long, slender optical tube of a refractor is the image that most people associate with a telescope. Refractor telescopes have the advantage of having an unobstructed light path, which produces higher visual contrast than other optical designs. Stars appear as pinpoints against an inky black background when viewed in a refractor. Refractors have the disadvantage of being the most costly per unit of aperture, which is why refractors tend to be smaller than all other designs. Newtonian Reflector TelescopesNewtonian reflector telescopes are an optical design that use a mirror to focus light into a smaller area. Most of the larger telescopes in use today utilize mirrors for economic reasons. It is less expensive to produce a mirror than a lens, and that advantage grows with the size of the telescope. The main advantage of a Newtonian Reflector is cost per unit aperture. The disadvantage is the images they produce are upside down, meaning that they are not suitable for terrestrial observing. Dobsonian TelescopesA Dobsonian telescope is a Newtonian reflector mounted on a simple yet stable alt-azimuth (lazy Susan style) mount. These telescopes are named for their designer, John Dobson, who sought to build a low cost large aperture telescope. No other design has had a greater impact on amateur astronomy in the past half century. Dobsonian telescopes are popular because they offer the most available aperture for the dollar. Dobsonian telescopes may appear unconventional to the first time buyer, but the fact is that they dominate the market for amateur telescopes over eleven inches in aperture. Wikipedia has a fine article on the history and origins of the Dobsonian Telescope. Schmidt-Cassegrain TelescopesSchmidt-Cassegrain telescopes use both mirrors and a lens (corrector plate) to focus light into a smaller area. Schmidt-Cassegrains are popular due to their compact size relative to their aperture. These are the Jack of all trades in the telescope business. They are moderately well adapted to a wide variety of applications, including lunar, planetary, deep space, and even terrestrial observing. Variations on the Schmidt-Cassegrain design include Celestron's EdgeHD and Meade's Advanced Coma Free (ACF) optical systems. The primary advantage of a Schmidt-Cassegrain telescope is that it tends to offer the greatest degree of portability per unit of aperture. The disadvantage is they are more costly than Newtonian Reflectors. Maksutov Cassegrain TelescopesMaksutov-Cassegrain telescopes are similar to Schmidt-Cassegrains, using both mirrors and a lens to focus light into a smaller area. Maksutov-Cassegrains replace the flat corrector plate of the Schmidt-Cassegrain with a convex meniscus lens. The secondary mirror is actually a silvered spot on the inside of the meniscus lens. This in itself leads to one major advantage: Maksutovs do not require periodic collimation of the optics as do Schmidt-Cassegrains and Newtonians. Maksutov-Cassegrains offer superior contrast to a Schmidt-Cassegrain, but they are also more expensive per unit of aperture. What not to buyWe've touched upon this subject above, but Sky & Telescope magazine has published an excellent article on this topic. There is one point in this article that cannot be given enough emphasis: avoid what is called the “Bird-Jones” reflector telescope. This advice is far easier to give than to follow, as these telescopes are never labeled this way. The easy way to tell if a telescope is a Bird-Jones reflector is to compare the physical length of the optical tube to the focal length. These two figures should be relatively close, albeit one is likely to be stated in inches and the other in millimeters. One inch equals 25.4 millimeters. Bird-Jones reflectors typically have an aperture of 114 or 127 millimeters with a focal length of 1000 millimeters. If you see something advertised as a Newtonian reflector that appears to be short and stubby, run, don't walk away! PhotographyTaking pictures with a telescope means different things to different people. You can simply aim a smart phone camera into an eyepiece and get a pretty decent image of the moon or even Saturn. If, on the other hand, you want to try to capture images of galaxies and nebulae, the subject is much more complicated. This may seem counter-intuitive, but the most important piece of equipment needed for professional quality results is neither the telescope nor the camera. The most important piece of the puzzle is the telescope mount, because without a mount that can track a target smoothly and accurately for minutes at a time, it will be impossible to achieve an adequate exposure. Pictured at right is an example of a telescope that is suitable for astrophotography. The first thing you may notice is that the mount looks nothing like any of the other telescopes pictured on this tutorial page. This telescope features a German equatorial mount that when properly aligned will precisely follow an object as it traces its natural arc across the sky. Using such a mount requires a precise alignment of its rotational axis with the Earth's own rotational axis. We call this "polar alignment" and it is something that the beginning visual astronomer doesn't need to be troubled with. It isn't all that difficult to do, provided that you understand the concept. Plan on spending at least $800 for a quality telescope mount alone, or $1500 for a complete system such as the one pictured in order to attempt any serious photography. There are a number of good introductory books on this topic here on this website, and we would strongly encourage you to read one before heading down the astrophotography path. Planetary photography is a subject unto itself, and one that requires different equipment and techniques than those used to capture deep space objects. Astrophotography is a highly rewarding part of this hobby, but to do it right requires a higher level of commitment than many beginners realize. It's not that we want to discourage you, but we do think it important that you approach this topic with realistic expectations. About Skies UnlimitedSkies Unlimited was founded in 2004 with the object of making the telescope buying experience both easier and more enjoyable. We have helped thousands of people like you to select the right telescope to meet their specific needs. Our staff of real amateur astronomers actually use the telescopes and accessories we sell and can give you honest advice on their suitability for your particular needs. At Skies Unlimited we offer a broad selection, including used telescopes, all at low prices and with practical honest advice. If you are unable to find the answers you need here, then by all means give us a call. More Reading on TelescopesThose of you with a real thirst for knowledge with respect to telescopes, both amateur and professional, may want to start Wikipedia's broad based coverage of the topic, including many links to other articles, at wikipedia.org/wiki/Telescope. Keep in mind that you do not need to know how telescope optics work in order to enjoy them. NASA maintains a website dedicated to the Hubble Space Telescope at www.nasa.gov/hubble/. This website includes the history and technical details of the telescope, as well as a gallery of images. Please keep in mind that the Hubble telescope is much larger than any amateur telescope and that it is not encumbered by the negative effects of the Earth's atmosphere. Hubble images will invariably be better than what can be seen with an amateur telescope, but the experience is just not the same as seeing an object with your own telescope. |