Telescope Advice

Stellarvue

Telescope Recommendations

1. Overall, I think the best telescope for the money is the $550 Orion Telescopes 8-inch diameter Newtonian reflector with a digital hand display for finding objects. This is a manual scope that you move by hand, but the hand display tells you what direction to push the telescope so any object chosen from its database will appear in the eyepiece. You can purchase direct, but some telescope stores carry this model. If you purchase this scope or any other quality scope, it will be fairly easy to sell if you don’t like the hobby.

2. Refractors. I would look at Stellarvue for a good quality refractor. Tele Vue telescopes have THE highest quality optics but they are expensive (I own three Tel Vue scopes and love them—Ken Graun). Refractors often don’t come with a mount and tripod, so take a look at iOptron.

3. Hybrid Telescopes. The Schmidt-Cassegrain Telescope (SCT) is probably the most versatile and feature ladened telescope on the market. I prefer the Celestron brand over Meade. The 8-inch is the most popular size. These scopes are GOTO (Go-To), that is, they have computerized motors that will automatically move to and track any object selected from the hand controller (which has a display and lists thousands of objects, including all the planets).

Great Telescope Stores. Click here for a list of great telescope stores across the US.

Telescope Reviews. Click here for a link to telescope reviews.

Want Telescope Advice? If you have a question or would like advice on buying a telescope or accessory, please email me (Ken Graun) at AstroInfo. No charge, no obligation, no hassles.

Orion

Tele Vue

Celestron

The Three Basic Telescopes

Refractor

When most people think of a planet, they think of Saturn. When they think of a telescope, they think of a refractor.

A refractor is a telescope with a front lens that brings light to a focus at the rear of the instrument. Refractors were the first telescopes. It all started around 1608 when Galileo and other scientists heard about the invention and made their own instruments for astronomical use. Refractors were used extensively by astronomers until the early 1900s, when they were replaced by reflectors that were larger and less costly to build. The largest refractor in the world, completed in 1897, is the 40-inch diameter Yerkes refractor at Williams Bay, Wisconsin. Among amateurs, refractors have enjoyed a resurgence because their optical quality has im-proved dramatically over the past years.

The refractor attraction
Refractors are easy to use and practically maintenance free. Unless severely jarred, the optics may never need alignment. The only maintenance is an occasional cleaning of the outside front objective. Today, the tubes are physically shorter than they used to be, which makes these telescopes easier than ever to set up, use and store. Refractors are often the telescope of choice for astrophotography. Some of the best celestial photos have been taken with this type of telescope.

The down side
Refractors are great instruments to explore the heavens, but unfortunatly, inexpensive refractors have done more to taint first impressions of observational astronomy than almost any other factor. I have heard, firsthand, numerous reports of disappointment from people who purchased refractors from department stores, or purchased a lower line name brand model. The irony and “up side” to all this is that middle-of-the-line refractors perform better than ever and the top-of-the-line perform the best of any telescope.

Cost, APOs and size limitations
Per aperture inch, a quality refractor costs more than any other type of telescope. For example, for $3,000, you could purchase either a 4-inch quality refractor (without mount), a 15-inch Newtonian reflector (with mount) or an 11-inch GO TO SCT (with mount).

Although $3,000 dollars is a lot of money for a quality 4-inch refractor, a middle-of-the-line, good-quality, 3-inch refractor can be purchased for $400 to $1,000. The $3,000 refractor represents the highest quality type and is known as an APO (pronounced A-P-O, an abbreviation for apochromatic, which means “free of any optical aberrations”). These telescopes provide incredibly sharp images and for this reason, I enjoy looking through an APO telescope more than any other type of telescope.

The largest readily available diameter for refractors is 4 inches (100mm). Diameters of just 5 to 6 inches must often be special ordered, sometimes with waiting periods of several years.

Newtonian Reflector and the Dobsonian

The Newtonian reflector has been a workhorse for both professionals and amateurs since its invention in 1668 by Isaac Newton. This type of telescope has a concave parabolic mirror at the rear of its tube that focuses light to an eyepiece near the front end. Amateurs enjoy using reflectors more than ever, in diameters ranging from 4 to more than 36 inches.

Least expensive per inch
The Newtonian reflector is the least expensive telescope per aperture inch. Generally, this telescope is set on a simple, non-motorized mount, called an alt-az mount (short for altitude-azimuth), which moves up and down and rotates to any compass point, similar to binocular mounts at tourist attractions. The optics for reflectors with diameters of 10 inches or less are usually housed in tubes, while those with diameters of 12 inches or more are often placed in an open-frame, truss-tube assembly that can be disassembled and stored compactly (see pictures to the tight). An 8-inch Newtonian sells for about $500, a 10-inch for around $650.

Newtonian Reflector = Dobsonian
The word “Dobsonian”often pops up as a descriptive term for a telescope. A Dobsonian telescope is nothing more than a Newtonian Reflector on a simple altitude-azimuth mount. In the 1970s, John Dobson popularized simplicty in telescopes in order to make inexpenisve, big telescopes that could be used to introduce the general public to the night sky.

A little more maintenance
The Newtonian reflector requires occasional to frequent optical alignments, and occasional cleaning of its mirrors. Aligning or collimating the mirrors is easy to perform after you have done it a few times and there are specialty “tools” to aid in the process. Collimation must be performed after each assembly of truss-tube reflectors. The mirrors of reflectors need occasional cleaning because they are exposed to the elements. Depending on use and environmental conditions, yearly cleanings (or longer intervals) may be all that’s needed. Don’t worry about some dust on the mirrors, which is normal and does not affect viewing. About every 10 to 20 years, the reflective coating may need to be replaced.

“Light buckets”
The largest refractors are about 6 inches in diameter, compared to 14 to 16 inches for SCTs (see picture on right side), but the largest reflectors zoom to 36 inches. Large-diameter Newtonian reflectors provide the brightest images of galaxies and nebulae because they collect more light (hence the term “light bucket”) than their smaller counterparts. Image brightness depends on the surface area of the lens or mirror. A 20-inch-diameter Newtonian gathers over 11 times more light than a 6-inch lens or mirror.

Manual labor
Today, more than ever before, Newtonian reflectors are set on simple, non-motorized mounts. This can be a boon or, a bane depending on your orientation and intentions. These simple mounts have allowed manufacturers to hold down costs, enabling amateurs to afford the largest diameter telescopes ever. However, these telescopes are limited to visual use only and cannot effectively be used for astrophotography. Although it is possible to buy a mechanism that will allow these telescopes to follow celestial objects for short periods of time, for the most part they are manual and must be continually nudged to keep an object in view.

A little help from a friend
Newtonians mounted on simple alt-az mounts can be equipped with “encoders” and a hand controller to help find celestial objects. This allows the telescope to work similarly to the GO TO telescopes described below. The only difference is that you move the telescope by hand, watching directional arrows on the hand-controller’s display. Visit your local telescope store for more information. Once installed, these systems do work well.

Schmidt-Cassegrain Telescopes (SCT) & Other Hybrids

The Schmidt-Cassegrain Telescope (often called S-C-T) is the telescope of choice amongst amateurs, but what is it? Schmidt-Cassegrain is the name of an optical design inspired by Barnard Schmidt (1879–1935) and Guillaume Cassegrain (1625–1712). This type of telescope is often referred to as a hybrid because it contains elements of both reflecting and refracting telescopes. Like a Newtonian reflector, it has a rear primary mirror that focuses light, but it also incorporates a front lens or corrector plate that not only seals the tube from the environment but also helps to fold the optics, making this telescope very compact. The eyepiece holder is at the end of the tube, similarly to a refractor, but for the focused light to get there, it must pass through a hole in the middle of the mirror. This design has been so successful that a 5.5-inch diameter version made by Celestron has been used on Space Shuttle missions.

Computer automated GO TO technology
Today, a major attraction of SCTs is that most come with a mount incorporating computerized GO TO technology. This simply means that after you set up the telescope and align it to two bright stars (a five-minute process guided by prompts from a hand controller, detailed on page 52), the telescope will automatically move to and follow objects chosen from its huge database. These telescopes can even take you on a tour of the night sky, providing sights of the best objects visible from your location.

Other hybrids
There are several hybrid designs. The most common after the SCT is the Maksutov (sometimes referred to as the Maksutov-Cassegrain or just Mak), designed by the Russian optician Dmitri Maksutov (1896–1964). The SCTs and Maks look similar but the Maks have an actual lens in front, call a meniscus, that is thick and highly concave. Some people prefer this design because it performs optically a little better than SCTs. Maks are readily available in diameters of 3 to 4 inches, with larger diameters now becoming more available.

Best value, cost
Why are SCTs the telescopes of choice amongst amateurs? Simply because they offer the most features for your money. Manufacturers generally sell SCTs as turnkey systems, meaning that they include everything—the telescope on a computerized mount, the tripod, a finder and an eyepiece (you will have to purchase more eyepieces). And SCTs breakdown and store well. An 8-inch can easily be packed and hidden in a closet. The 8-inch is the most popular size and sells for about $2,400. I highly recommend this type of telescope if you can afford it.

Maintenance
For the most part, maintenance on SCTs and Maksutovs is minimal. Occasionally, the outside front element should be cleaned—at most yearly, but depending on use. The optics of the Maksutov are like refractors and are permanently aligned, whereas those of the SCTs may need occasional collimation depending on use and jarring by transportation. Collimating SCTs requires some skill and not all telescope stores can provide this service. Sometimes there are members of local astronomy clubs who can perform this adjustment.

The three most common telescopes use different means to bring light to a focus.

A 4-inch APO refractor by Tele Vue. Although this telescope is expensive, its optical quality is outstanding. It is mounted on a simple, non-motorized altitude-azimuth mount that allows up and down movement as well as rotation around the center axis. As pictured, this telescope lacks a finderscope for aiming at the sky.

A homemade 6-inch Dobsonian-type Newtonian reflector. The panel near the bottom end of the tube can be removed to clean the mirror.

A 15-inch-diameter Dobsonian-type Newtonian reflector.
This telescope features an open truss-tube design that reduces overall weight and facilitates assembly/disassembly for transportation or storage. With larger Newtonians like this, ladders are often needed to reach the eyepiece which is located near the top. Obsesssion is the name of one company that makes telescopes like this.

Below. A Celestron 11-inch diameter Schmidt-Cassegrain Telescope. Like most SCTs, this telescope comes complete with an integral mount and stand.

What’s Out Tonight? is sponsored by Ken Press, publisher of astronomy books and charts.
Phone: (520) 743-3200 • Fax: (520) 743-3210 • Email: ken@kenpress.com