Choosing A Telescope
Sometimes when friends or co-workers find out that I am involved in amateur astronomy they ask me what would be the best telescope to buy. It's not always an easy question to answer. There are many factors to consider, such as the kind of observing the person wants to do, the amount of money available to spend, if they can observe from home, or need to transport the telescope to the observing site, and the like. I try to offer suggestions based on the factors I have found important in choosing a telescope, such as optical and mechanical quality, portability, and ease of use.
Like many people, I started out with a small achromatic refractor. The first one was a 40mm refractor that I bought in 1972. It had a fixed magnification of 10x and I had to hand hold it but it did provide my first views of celestial objects. The next telescope was a 60mm refractor made by Jason, designed for terrestrial viewing and only gave powers up to 60x. It had terrible secondary color on bright objects, and the alt-az mount was not very stable. It cost $29.95 back in 1973, which was a lot for me at the time. But, it showed me the main cloud belts on Jupiter, and I watched its four Galilean satellites as they changed position night after night.
The fact I could see this on a planet that was over 480 million miles away really was amazing to me. Add to that the fact that I could see craters on the moon and I was hooked! It was with this telescope that I first began making sketches at the eyepiece of astronomical objects, which has come to be a lifelong interest for me. Here is the first sketch I made of Jupiter on August 13, 1973:
Still, I longed for a true astronomical telescope, one that could use higher magnifications and not have such bad secondary color. A friend of me led me to a garage sale one day where I found just such a telescope. It was another 60mm achromatic refractor, imported from Japan, and made by a company called Scope, aptly enough. But the lens was an air-spaced doublet, not a cemented doublet like the Jason, and the telescope came with slow motions controls on both axes. Best of all, it could be used at higher magnifications and give clean, crisp, and contrasty images.
With this telescope I was able to resolve more detail on Jupiter, including a shadow transit of one of its moons. Also I was able to see the Great Red Spot even though I could not quie make out the red color in a sketch I made on September 5th, 1974 as shown below:
Mars, during the favorable opposition of 1973 where its diameter reach 21.47", showed some of the larger surface features in this telescope, such as Mare and the South Polar Cap.
I observed Saturn for the first time, which I remember to this day the beauty of its rings. In addition I observed M-13 for the first time, and my first deep-sky sketch was of this cluster.
So the first lesson I learned was that just because two telescopes were of equal aperture did not mean they would perform the same. I realized early on the importance of optical and mechanical quality and stable mount.
Soon I got aperture fever, and my next two telescopes were Newtonian reflectors on German equatorial mounts. The first was a used Edmund 4-1/4" f/10. It didn't have rotating rings so I added them to make it more convenient to position the telescope while observing. Through this telescope Jupiter's Great Red Spot lived up to its name, and the Orion Nebula, M-42 was a beautiful green glowing gas cloud. The equatorial zone on Saturn was visible, as was the Cassini division.
Part of the advertisement for the Edmund 4-1/4" f/10 reflector that I purchased used in 1974.
Then in 1975 I sold both of the 60mm refractors and the Edmund reflector and ordered a Criterion RV-6 reflector with an electric clock drive. It cost $263.45 including eyepieces, and took seven months to arrive, but it was one of the best telescopes I ever owned. It came with rotating rings, which made it easier to adjust the tube to a comfortable viewing position, and the clock drive made it more convenient to observe and make drawings of the planets.
The optics were also quite good, and it was the best planetary telescope that I owned up until I began using apochromatic refractors some years later. One night in 1977 when Saturn was at opposition and high in the sky with an altitude of 65°. The seeing conditions were excellent, and I was able to use a magnification of over 100x per inch of aperture using Orthoscopics eyepieces and the image was still sharp, contrasty and with very little image breakdown according to the notes I made with the sketch that night. It was one of the most memorable views of Saturn I have ever had. The Moon, Venus, and deep-sky objects including M-13, M-31, and M-42 all look very fine in it.
Part of the advertisement for the Criterion RV-6 reflector that I purchased in 1975.
As time went on however I didn't get the chance to use the RV-6 as much as I would have liked, and wished for something more portable that I could set up more easily. This was around the time that Celestron first started to introduce their C90 MCT. The spotting telescope version could easily be mounted on a photo tripod for easy set up and use. So I sold the RV-6 and purchased the C90 and a pair of University Optics 11x80mm binoculars. I figured even with less aperture I might observe more often with a portable telescope, and the large binoculars would aid in finding objects I had not seen before.
As it turned out, I was able to observe more often with this portable setup, but the optical quality of the C90 was only fair at best. Also I did miss the larger aperture of the old 6" reflector. I did have a chance to compare the C90 with a Questar 3-1/2" MCT on several occasions, and the Questar had noticeably better optics. Plus I loved the built in barlow on the Questar, as well as the star chart and Moon map on its barrel and dew cap.
So the second lesson I learned was that while optical quality is very important in any telescope, the portability of a telescope may determine how often it gets set up and used. The best optical telescope in the world may not get used very often if it is difficult to set up.
Closeup photograph of Celestron 8 with Meade 4" SCT piggybacked on top. The finder was University Optics 8 x 50mm right angle correct image finder. To reduce the likelihood of dew forming on the corrector plate a heating element was wrapped around the front of the tube assembly and secured with duck tape. It was low tech, but it worked.
In the late 1970's C8 SCT's were becoming more popular, and seemed to offer both the optical quality and portability that I was looking for. So in 1980 I sold the C90 and bought a C8, and found that for an 8" telescope it was indeed reasonably portable. It showed more detail in deep-sky objects than my old RV-6 6" reflector, and was easier to set up and use. Also, it was much easier to use for astrophotography then the reflectors I had owned. While the optics seemed good, I felt the optics in the RV-6 had were better, and so when it came to the planets I felt that the RV-6 did a better job. The RV-6 showed the planets with higher contrast, and also brought out low contrast detail better. Also, the open tube of the reflector adjusted to the nighttime air faster then the closed tube of the SCT.
So the third lesson I learned was that larger aperture does not necessarily mean a telescope will outperform a smaller one when it comes to the planets, particularly when it comes to showing fine, low contrast detail. Optical quality is important regardless of the aperture.
It was with the C8 that I caught the astrophotography bug. These older-model C8's had a spur gear drive system, which were not very accurate, so it made doing astrophotography very trying. A friend of mine said it built character, but I told him that it wasn't the kind of character that I wanted to build. So I invested in a more accurate Kencor worm-gear drive to replace the spur-gear drive, as well as other accessories to get consistently good results, including a Lumicon film hypering kit and off-axis guider, guiding eyepiece, dew removal system, and Astro-Physics dual axis drive corrector. Plus trying to find a color negative film that had both good red and blue sensitivity.
For a while I thought about buying a larger SCT such as a Meade 10" so I could record finer detail in my astro-images. I visited a local telescope store where one was displayed and while talking to the salesman I picked up the scope in its fork mount. I was surprised how much bulkier and heavier it was than my C8, and realized this might impact how often I wanted to set it up compared to my C8. Later I bought a Meade 4" f/10 SCT tube assembly that could be used on a small equatorial mount for a quick observing session or piggybacked on top of the C8 for astrophotography. The optics of the Meade 4" seemed to be very good.
A couple of years after I bought the C8 I had a chance to observe M-17 through a Quantum 6 at Stellafane one night. It seemed to show more detail then I expected for a long-focus 6" telescope, and the image was sharp and contrasty. I wondered why it did a better job then I initially thought it would on a deep-sky object, for I thought such were telescopes strictly for lunar and planetary observing. Then I read an article in the Winter 1983 issue of Deep Sky Magazine by Richard Berry entitled "Of Stellafane, Optics, and the Art of Deep Sky Observing". In it he mentioned some of the important characteristics of a telescope when it comes to performing well on deep-sky objects, such as low internal scattering, excellent optics, high image contrast, and wide field of view.
I realized then that telescopes of small to medium aperture, if well built, can sometimes do much better then one might expect on deep-sky objects.
As much as I enjoyed the results I was obtaining doing astrophotography, I missed sketching at the eyepiece, and the sense of connection that I got with an object while I observed and made a drawing of it. In the early 1980's Astro-Physics (AP) began to offer apochromatic refractors. Since I had bought my dual-axis drive corrector from them for my C8 and felt they made good quality equipment I decided to order a refractor from them, so I sold the SCT's and purchased an AP 4" f/6 in 1984. These early telescopes did have some secondary spectrum on bright objects, but I was very impressed by the wide, sharp and high contrast views they provided. It did a wonderful job on Comet Halley , as well as deep-sky objects. From a dark sky location the nuclei of both M-51 and NGC 5195, the satellite galaxy, appeared starlike, and it was possible to see the connecting arm between the two. Also, some dark rifts were visible around the central portion of M-51.
In 1986 I bought a 6" f/9 refractor from AP, and finally found a telescope that showed me more detail on the planets then any of my earlier telescopes did. In the following years I purchased a many other telescopes from them, including a 5.1" f/8.35 and a 7.1" f/9. Jupiter showed a wealth of fine detail, including faint belts and festoons, detail in the Great Red Spot, and its moons appearing as different sized disks. Saturn and Mars showed a wealth of very fine detail as well, including spokes in Saturn's rings, and equatorial cloud bands on Mars. Even deep-sky performance was impressive. M-42 was a mass of very fine mottling, and the it appeared more of a bluish color to my eye then the usual green I had seen in other telescopes. One night with very dark and steady skies the bottom of the nebula had a reddish color to it.
The TMB 175mm f/8 Refractor.
In 2004 I sold all of my AP telescopes including a 180mm f/9 EDT refractor, 130mm f/8.35 EDF refractor, and 90mm f/5 EDL refractor and replaced them with three apochromatic refractors from TMB Optical: a 7" (175mm) a 5.1" (130mm) f/9.25, and a 4.1" (105mm) f/6.2. The TMB are among the most optically and mechanically impressive telescopes I have ever owned or used, with the Feather Touch Focuser making it very easy to focus the telescope even at high power.
I have owned larger telescopes in the past, both of them reflectors. One was an old 12.5" f/6 Cave on a heavy German equatorial mount. Even broken down into its smallest components it was a very large and cumbersome instrument to set up, and I did not have a place to keep it permanently. I still wanted more aperture, but realized this wasn't the way to go. So eventually I invested in a 20" Obsession. Dave Kreige of Obsession Telescopes has really done a very fine job of designing and building these telescopes. They are the closest I have ever seen to equaling the performance of a refractor. They offer fine quality workmanship and optics, portability, ease of set up and use, and very fine views of deep-sky objects and the planets.
The StarMaster 14.5" f/4.3 reflector.
The same holds true with Rick Singmaster of StarMaster. The Starmaster 14.5" reflector that I owned was one of the best designed telescopes I have ever had the pleasure of observing with, offering large aperture with very fine optics in a highly portable package that is easy to set up and use. In addition with the ability to add tracking and GOTO it is makes it easy to locate deep-sky objects even under less than ideal observing conditions.
In my opinion, we live in a fortunate time for amateur astronomy. There are many choices, far more then when I got started many years ago in the late 1950's. Back then a typical starter telescope was a 60mm achromatic refractor. If you owned a 6" or 8" reflector on a German equatorial mount it was really something. Maybe you had a friend who knew someone who knew someone else who had a 10" reflector or 4" or 6" achromatic refractor, but it wasn't very common. Then came the SCT revolution, the Dobsonian revolution, and the apochromatic refractor revolution. Now an 8" telescope, like a SCT from Celestron or Meade, is very common, as are 4" through 6" apochromatic refractors, from companies like Astro-Physics (AP), TMB Optical (TMB), and Tele-Vue (TV). Also many people own or have access to large-aperture Dobsonians. Not to mention the revolution in high quality eyepieces, better film for astrophotography, CCD cameras, equatorial platforms, and computer controlled telescopes.
It can seem very overwhelming, particularly if you are just trying to get started in this hobby. The best advice I can give is to start slowly. Buy a good introductory book on astronomy. One such book is by Terrence Dickinson, and is entitled Nightwatch. It is available at most bookstores like Barnes and Noble or from Sky Publishing. Also, consider subscribing to the following magazines: Astronomy, Sky & Telescope, or Amateur Astronomy. Begin to learn the sky with the unaided eye. Rather then buying a large expensive telescope immediately, consider buying or borrowing a pair of binoculars or small telescope first.
If you have never looked through a telescope before and you know someone who owns one ask if you can observe with them some night. Or go to a star party and try viewing through different telescopes. Offer to help set up their telescopes, and ask them what they like or dislike about their telescopes and why. This may give you an idea as to the optical and mechanical quality of the telescopes that are available, as well as their ease of set up and use. You can get an idea as to the kind of optical accessories they use as well, such as eyepieces, finderscopes, filters, or star diagonals. Then decide what it is you like to observe, what telescope may best suit your needs, and go from there. There are a number of online astronomy chat groups that can sometimes offer valuable suggestions as well.
Whatever telescope you decide to buy, try to buy the best optical and mechanical quality one you can afford, regardless of its aperture or design (such as a SCT, MCT, refractor, reflector, or hybrid), and one that fits your portability and ease of use needs. If a telescope is too big, or too much of a hassle to set up, you won't use it very often. For example, if you live in an apartment and have to carry your telescope up and down many flights of stairs just to use it, a smaller more portable telescope may be a better choice then a larger one. If you live in a place where all you have to do is open your back door and carry your telescope out to start observing, a larger aperture telescope may be a good choice. Regardless of the aperture or portability of a telescope, the optical quality is important, because if the optical quality is poor you may not end up using it very often.
Remember, too, you don't need the latest 25" telescope from Celestron, Meade, Obsession, StarMaster, Questar, TMB, AP, TAK, TEC, or other manufacturer to enjoy the night sky. It can be done with some very modest equipment. If you buy a telescope and decide you want to get a larger aperture one someday you can, and use all of the skills you learned with the smaller instrument.
Finally, remember that whatever telescope you choose, the only real important thing is if you enjoy using it. It is tempting in any hobby to always want the latest and greatest equipment. In astronomy this would be to always want the latest or greatest telescope, or eyepiece, or accessory, or CCD camera, to keep up with the astronomical Jones's of the world. But it is also very easy at the same time to lose sight of what initially sparked our interest in the night sky (or daytime sky, if you are a solar observer) in the first place. The universe is a wondrous place. So the main thing is to enjoy it, with whatever equipment you choose.
Article © 2000 - 2013, Eric Jamison, All rights reserved.