Don't Buy a Big Telescope!
By the Astronomy and Photography Online Staff
This list of the largest optical reflecting telescopes with objective diameters of 3.0 metres (120 in) or greater is sorted by aperture, which is one limit on the light-gathering power and resolution of a reflecting telescope's optical assembly. The mirrors themselves can be larger than the aperture, and telescopes may use aperture synthesis achieved by interferometry.
The Celestron C6, an excellent telescope. Illustration courtesy of Celestron International.
This article is directed at novice astronomers, meaningamateurs buying their secondtelescope (or first 'serious' scope) after discovering that theirinitial instrument, probably a 60mm refractor or cheap table top Newtonian,lacks sufficient light grasp for viewing many deep sky objects. It should alsoserve as a warning to more experienced astronomers getting back into the hobbyafter a significant lay off: scopes have gotten bigger while you were away!
Let's get 'big' defined from the outset. In termsof portable astronomical telescopes, the heaviest optical tubes should weigh nomore than about 20 pounds (assembled). They should be sufficiently compact tofit in the trunk of an ordinary sedan and fit on mounting systems that can betransported and assembled quickly by one person without physical strain. Whilementioning mounts, whether equatorial (EQ) or alt-azimuth (AZ), they shouldhave precise slow motion controls that allow accurate and easy alignment of thescope with objects in the night sky. The biggest scope in the world is uselessif you cannot accurately point it at a target and keep it there as the earth turns.
There is a trend in recent years for novice astronomers togo overboard and purchase very large telescopes. (Anything with an apertureexceeding eight inches is very large for our purposes.) Seeking to remedy alack of light grasp, they err in the opposite direction and buy a telescopethat is too complicated to assemble and collimate, too big, clumsy, heavy anddifficult to transport. They exacerbate the problem by accepting a crude AZ mountingsystem, often made of wood and lacking slow motion controls or any method ofprecisely tracking celestial objects.
We recently heard about a novice who purchased a 16' truss-type Newtonian refelctor. This particular scope comes with a wooden Dobsonian mountwithout any slow motion controls or tracking capability. The assembled opticaltube weighs 74 pounds and the mount weighs 54 pounds. Itmust be completely disassembled for transport and reassembled before use. Afterassembly, the primary and secondary mirrors should be collimated, a laboriousprocedure, especially for a novice. It would be hard to imagine a poorer telescopefor a novice, but the story illustrates the 'aperture fever' that isrampant in our hobby.
A friend purchased, after listening to the advice of supposedly knowledgeable amateur astronomers, a 10' aperture Newtonian, also on a Dobsonian mount. That scope got used about three times before the owner realized that he was spending more time assembling and collimating his scope than observing with it. He soon switched to a 90mm APO refractor and has never looked back. He later told us, 'No one told me that the 10' Dob was a pain in the knees, back, neck and patience; it gave brighter, blurrier images than the 90mm APO.'
The point of these sad stories is that telescopes can just as easily be too big as too small. A subtext is that quality, both optical and mechanical, is more important than quantity (raw aperture). A good quality scope of moderate size will usually reveal more detail about the wonders of the universe than a big, crude scope.
Try to learn at least something of the night sky with your very first telescope,regardless of its inferiority to the scopes the guys in the club own, before you upgrade. You canuse practically any telescope, even a terrestrial spotting scope, inconjunction with a star map and a binocular to learn how to star hop. Learn howtelescopes, eyepieces and mounts work. Learn how to quickly align an equatorialmount, at least close enough for casual visual observation. (We are doing a briefarticle about that.) Alignment is not difficult and should not take a lot of time.Achieve this modest level of expertise beforeyou upgrade to an intermediate level telescope, so that you can make an informed decision.
When you decide to upgrade to a 'real' telescope,resist the temptation to plunge into an advanced level instrument that is larger,more complicated and more expensive than you really need. For help on choosinga new telescope, see our article 'Guideto Beginner, Intermediate, Advanced and Expert Astronomical Telescopes.'which can be found on the Astronomy andPhotography Online index page.
A good example of an appropriate step up from the usual entry-level telescope is the Celestron OmniXLT line. This is a line of intermediate level telescopes that are reasonablypriced, well designed and engineered, well made and supplied with an equallygood German EQ mounting system. Sky-Watcher, Orion and Vixen offer equivalentmodels and mounts that will not break the bank. All Omni XLT telescopes includea manual CG-4 mounting system with precise slow motion controls. Omni XLT telescopesinclude 4' achromatic and ED refractors, a 5' Schmidt-Cassegrain(SCT) and a 6' Newtonian. Any of these would make good novice/intermediate telescopes.
For the affluent novice, a Stellarvue or Tele Vue APO refractor in the 90mm to 105mm clearaperture range, or a Questar 3.5' Standard Maksutov-Cassegrain would be hard tobeat. These scopes are so capable that you may never want, or need, to upgradeagain. If you later add a larger scope, you will want to keep the smaller scopeand if you don't, you will be sorry.
The upper limit in aperture and physical size that most novice astronomers should consider is a high quality 6'-7' catadioptric (CAT), 6' Newtonian reflector or 4.5'-5' APO refractor. These are very capable telescopes, many of which are considered advanced level instruments. They will often out perform larger telescopes in the field. The Celestron C6 (a 6' aperture, 1500mm focal length SCT) might be the ultimate telescope for the serious novice. It is economical, compact, lightweight and very capable. It can be purchased as an optical tube assembly (OTA) and mated with a manual CG-4 mount (also available separately), or bundled with a CG-5 (computerized go-to) equatorial mount. Either way, you have a very flexible telescope system with plenty of room to grow.
The absolute biggest telescope a novice should buy is an 8', f/10 CAT, which is a very powerful instrument. The Celestron C8 has been around for some 50 years and is the most famous of these, although competing models are offered by Vixen and Meade. (There are a couple of C8 reviews on the A&P Online index page.) A C8-XLT is about 10' in diameter, 17' long and weighs 12.5 pounds. This scope requires a substantial German equatorial mount, such as a Celestron CG-5 or Vixen GPD2. These advanced level scopes are probably a little too much for the average novice, unless he or she is already a dedicated observer.
Whether you choose a medium priced model from Celestron, Sky-Watcher, Orion or Vixen, or a high priced model from Stellarvue, Tele Vue or Questar, the telescopes recommended in this article are portable, easy to use and allow the novice to grow in the hobby. In a nutshell, they are the kind of scopes that get used. Many expert astronomers are using the same or similar telescopes. They know scopes that are easy to use get used, while the giant dinosaur-scopes languish in storage.