Equipment

Once you have begun learning the sky, you can start thinking about equipment. As far as things go, astronomy is generally done with binoculars and of course, telescopes. I’ll deal with binoculars first, because they are probably MORE useful to a beginner than a telescope to start off with, for reasons I’ll explain below.
However, first a vitally important point about any piece of astronomical viewing equipment:
BE CAREFUL WHEN BUYING ANYTHING FROM A DEPARTMENT STORE, ESPECIALLY TELESCOPES!!!

Department stores are notorious among astronomers – they usually sell low quality, poorly constructed and poor performing binoculars and telescopes. Especially beware of advertisements for 500+ x magnification on small scopes. While they can theoretically achieve high magnification, the images stink. When it comes time to buy, go to a telescope store, or at least a photographic shop. Especially beware of the brand names Tasco, Jason, and Simmons. They are cheap, they are not solidly constructed and their optics are not terribly good.

 

BINOCULARS
It is best to start with binoculars: They are inexpensive, offer a wide field of view, and allow you to use both eyes for viewing, rather than just one. They are also portable, require little maintenance, you can use them for both land and sky viewing, and best of all, they are easy to use.
There are several important things to think about regarding binoculars:

The most important thing is aperture: how large (wide) the lenses are. The more aperture there is, the more you will see – i.e. you want them to let in plenty of light. The front lens(es) by the way, are called the objective(s), which generally means the primary optical device(s).

The next consideration is coating of the lenses. Binoculars are typically multi-coated, or fully coated. The coating refers to special optical solutions applied to the lens at the factory that help reject stray light, and help cut down on false colour, which has traditionally been a major problem for lens based optical equipment. Multi-coated optics have optical solutions on all lenses that are exposed to air, but generally do not offer colour correction (removing false colour) that is as good as fully coated optics (several layers of coatings on all lenses).

The third point relates to what you will be able to see through binoculars, and refers to two concepts, plus the involvement of aperture: The magnification of the binoculars (one concept), the aperture of the lenses, and the field of view (the second concept).

To help put this into perspective:

Have you ever seen what looks like a mathematical formula on a pair of binoculars, such as 10 x 50 7º ?

What this really refers to is the magnification of the binoculars e.g. 10 x or ten times, the aperture of the lenses e.g. 50mm (a common size), and a field of view of 7 degrees, which is quite wide. Ideally, you want a field of view as wide as possible: this helps you to fit objects into the picture: for example, on my binoculars, I can fit the entire Southern Cross into my FOV.

I use fully coated Yashica 10 x 50 7ºs for my binoculars. They are over 15 years old now, but still deliver (in my humble opinion) outstanding views.
Binoculars have widely varying magnifications and objective sizes: Typically, they range from about 8 x 25 to 25 x 80, though there are some larger ones.

When you are out observing with binoculars, your arms will start to get tired after a while, as will your neck from looking up: so it helps if you can mount your binoculars on a stand. Some places that sell binoculars also sell stands for them, or you can make your own. Stands are mandatory for large binoculars, such as 25 x 80: I don’t know anyone who can hold them steady after 5 minutes, as they weigh so much.

The wide fields of view offered by binoculars allows you easily fit whole sections of constellations and entire star clusters into an image. This wide field of view is also very helpful in locating objects, especially if a particular one that you want to see is hard to find.

Binoculars can also offer very good contrast. On an average night, I can easily find many deep space objects just by noticing their image against the sky as opposed to a star.
When you look at the moon however, the flat, dark grey areas (“mares” or “seas”) stand out incredibly well from the brighter cratered and mountain regions. Binoculars also cool down in the night air quickly. With telescopes (discussed soon), some time must be spent waiting for heat waves (that distort the viewing) to dissipate.

There are two basic types of binoculars: Porro Prism and Roof Prism.

Porro prisim
Porro Prism binoculars are historically the most common design. Light coming in through the objectives is focused by a pair of prisms so that the path is folded in a zig-zag pattern, and out through the eyepiece, which also ensures that the image comes out the right way up.
Porro Prism binoculars can be quite rugged. If the binoculars receive a good deal of knocking around however, or are dropped, the prisms can come out of collimation, or alignment. With the light path now skewith, the image will be somewhat blurred, or you may not be able to see anything. Fortunately, they can be realigned, though repairs should be handled by someone who knows what they are doing…

Roof Prism Binoculars
Roof Prism binoculars are a more modern design. Instead of “folding” the prisms and zigzagging the light path, Roof Prism binoculars allow for a “straight through” design, which helps prevent tenuous loss of light. They are also able to better withstand the knocks.
Because of their straight through design, Roof Prism binoculars can be made into compact sizes: generally speaking, many of the smaller size binoculars of today such as 8 x 25 are of Roof Prism Design.

TELESCOPES
Telescopes come in a very wide variety of types, shapes, and sizes. Before I get into specifics however, there are a few vital considerations:

As with Binoculars, the most important consideration is APERTURE. Aperture is even more important for telescopes than binoculars, and I’ll explain why later.
Before acquiring a scope, think about what you will want to see with it. Some scopes are best suited to the Moon and Planets, others for deep space objects.
Don’t rush to buy a telescope. Talk to owners, look through their scopes, and try out a variety first. You may find that the right scope for you is different from your expectations.

Just before we get the the good part about telescopes, there are some telescope mounting considerations:

Bases

There are three kinds of bases commonly available for mounting a telescope on: Tripod, Dobsonian, and a Permanent Pier.

Tripod

This is without a doubt the historical type of mount for amateur astronomy. Little needs to be said, other than to look for two main things in a tripod: A solid, stable construction (try to get wood over lightweight aluminium, unless weight is really an issue), and a compact design for portability.
A tripod is illustrated in the refractor picture below. However, a tripod is potentially the least stable design, when compared to the other mounts.

Dobsonian

This type of base is also a mount. It is named after an astronomer who popularized the design. This is little more than an open box placed on a free rotating platform. The telescope has large knobs fixed to the side of it that rest in curvatures in the top of the box when the telescope is placed into the mount, as is illustrated in the picture of a reflector telescope below. The telescope can move up and down (be moved in altitude), and be rotated left to right (be moved in azimuth). Movement in altitude and azimuth means the telescope has an altazimuth mount.
The Dobsonian mount is almost rock solid, and as simple as can be.

Permanent Pier

This is where a pylon (pier) is secured to the ground, and the telescope is mounted on top of it.
The pier is also very solid, especially if the base is on concrete.

Mounts

Except in the case of Dobsonian mounts, which are both base and mount, other telescopes have a separate base and mount. Mounts also feature controls (called slow-motion controls), that allow a user to manoeuvre the telescope on its mount. However, Dobsonian mounts do not have these controls. The telescope is moved by hand.

The mount is what connects the telescope to the base. There are two types of mount: Altazimuth, and Equatorial. One thing I want to stress at this point: Virtually any type of telescope can be attached to either type of mount.

Altazimuth mount

Altazimuth mounts, as already explained, allow the telescope to move in altitude (up / down) and azimuth (left / right). An altazimuth mount is shown in the picture of a refractor below. When using an altazimuth mount, you can just set up and go. Altazimuth mounts are not suited to astronomical photography except for quick snapshots, unless a field de-rotator (see the Photography Page) is used. Even then, photography is not the forté of the altazimuth mount because it does not easily allow tracking of objects across the sky.

Equatorial mount

Equatorial mounts allow a user to track an object as it moves across the sky (due to the Earth’s rotation). Whereas altazimuth mounts only move in altitude and azimuth, equatorial mounts can function in a similar way, but are used almost exclusively in right ascension and declination.
Right ascension means that the telescope can track an object as it moves across the sky, from east to west. Declination allows a telescope to follow the rising and setting of an object.

Essentially, right ascension is equivalent to longitude on the Earth, and declination is the same as latitude. Celestial co-ordinates, or the position of an object in the sky is given in right ascension and declination co-ordinates. To use an Equatorial mount, you must first polar align the telescope, to make sure that tracking will be done accurately, as objects seem to rotate around the poles. The further north or south one is, the more pronounced the effect.
Polar Alignment is done by lining your telescope exactly (or to within half a degree or so is usually good enough) with the north or south pole respectively, depending on which hemisphere you are in. You will need to adjust setting circles which are dials with hours, minutes, and degrees to match your latitude.

Using the slow motion controls, you can manually track an object. However it can be more fun (and less work) to attach a motor to your mount, and have it move the telescope for you.

Equatorial mounts are more complex than altazimuth mounts, but they are useful for doing photography, where an object must be tracked.

Computerized Telescopes

I will discuss these in more detail on the Going Further page, but for now, a simple explanation is due. Most small telescopes are manually driven – the user does the work of finding an object and moving slow motion controls etc. to keep the image in the eyepiece. Computerized telescopes however, make use of electronics and motors to do the finding of an object and the tracking of it for you. These two functions are huge advantages to computerized telescopes. The most popular example I can think for for an amateur astronomer is the Meade LX200. Having a computerized telescope means you don’t actually have to learn the sky – however, it is highly advisable! The only downside to a computerized telescope is the cost. They can be rather pricey.

Now we are ready to discuss telescopes proper.
So without any more ado:

The are fundamentally three different kinds of telescope, classified by their optical arrangements, with each kind having various subtypes. The three primary kinds are are Refractors, Reflectors, and Catadioptric.

Refractor
This is probably what most people think of when they hear the word “telescope”. Refractors use their objective lens to focus incoming light to a point.
The light rays converge at a diagonal prism or mirror, that reflects the light rays up through the eyepiece. Refractors can be used for either astronomical or land (terrestrial) viewing. For terrestrial viewing, the image actually appears upside down, and perhaps inverted right to left. To correct this, an erect image focuser needs to be used, instead of the 90 degree astronomical focuser. The focuser is the 90 degree device you see at the back of the telescope. The eyepiece is attached to it, and the focuser can be moved in and out (forwards or backwards) until image focus is achieved.

Refractors are the simplest type of telescope, and require little maintenance. This is reflected by the fact that they do not really require collimation of the lenses; they are fixed, just like binoculars (unless knocked around a lot). Refractors tend to typically have smaller objectives than the other types of telescopes, mainly because it is expensive and difficult to produce high quality lenses in larger apertures.

Aperture sizes commonly vary between 60mm (2.4″) to 178mm (7″), though a few are more. The most common sizes are 60mm (2.4″ most common), 70mm (2.9″), 80mm (3.3″ common), 90mm (3.5″ also common), 102mm (4″), 127mm (5″),152mm (6″) and 178mm (7″). The latter four larger apertures are generally (but not exclusively) reserved for very high quality refractors that use lenses made of ED (Extra low Dispersion) glass and / or special coatings (such as magnesium fluorite) that provide images virtually free of false colour (apochromatic). Smaller refractors frequently suffer from some false colour, often a shade of blue or violet when looking at stars and planets.

Refractors can best be used to advantage on the moon and planets. Despite false colour problems (in smaller, non-apochromatic scopes), refractors offer high contrast, which is an advantage when looking at these objects. For example, when looking at Jupiter, it becomes relatively easy to discern different bands around the planet.
Refractors can also be used on deep sky objects, but are not as good as reflectors, because their generally smaller apertures do not let in as much light.

Reflector
Whereas refractors use lenses to focus light, reflectors use mirrors. Reflectors have many designs, but I’ll look at the most common two: the Newtonian (illustrated), and the Cassegrain.

As a whole, reflectors share certain properties. Among the advantages, reflectors do not generally suffer from false colour like most small refractors do (i.e. they are apochromatic), because light is reflected, which means that light of different wavelengths (colours) do not get bent differently.

Reflectors, by nature of design, allow for large apertures at reasonable price, which is one important factor most astronomers look for (remember, the more aperture you have, the more light you will let in, and so the more you will see).

However, reflectors generally require more maintenance than refractors, because they come out of collimation more easily. The Newtonian design is best known for this, but it happens less frequently on Cassegrains too. Fortunately, re-collimation is an easy job that can be done in a matter of minutes (or seconds).

Aperture in the case of reflecting telescopes refers to the diameter of the main mirror (the primary mirror). Sizes vary from about 76mm (3.1″ xxx) to 915mm (36″), or more. The most common sizes for commercially made reflecting telescopes are 152mm (6″), 203mm (8″), 254mm (10″), 318mm (12.5″) and 406mm (16″). There are larger sizes, but they are less common. The biggest aperture telescopes are made by companies specializing in large sizes, or are home made.

 

Types of telescopes

Here is a better description of Newtonian and Cassegrain telescopes:

Newtonian

A Newtonian telescope is illustrated in the picture above, and in the one next to a refractor. Newtonian telescopes are named after Isaac Newton, who pioneered the design. In a Newtonian scope, light comes in through the open ended tube, and hits the primary mirror. The primary reflects this light to an angled, smaller mirror (called the secondary mirror) which reflects the light at 90 degrees though the focuser and the eyepiece.
Newtonians have one major disadvantage: because of their optical arrangement, images are always inverted, and so they are not well suited to terrestrial viewing.

Cassegrain
Cassegrain telescopes also use a primary and secondary mirror, but the light eventually gets focused out the back of the tube, like in a refractor.
As in a Newtonian, light enters through the open tube, and strikes the primary mirror. The light is then reflected to the secondary. However, the secondary is mounted in braces at the other end of the tube, and is mounted in such as way as to reflect light back towards the primary. The primary mirror in a Cassegrain has a hole in the centre, that allows the light to pass through it, into the focuser, and up through the eyepiece. The arrangement looks the same as the catadioptric telescope below, but there is no lens involved.

Reflectors are well suited to deep space work. While they can provide fine views of the Moon and planets, contrast is not generally as good as a refractor, due to the secondary mirrors and their holders partially obstructing the light coming in. However, when looking at star clusters, galaxies, and nebulae, reflectors can really use their larger aperture to advantage. My own scope is a 152mm (6″) Newtonian on a Dobsonian mount. Newtonians on a Dobsonian mount are often just called “Dobs”..

 

Catadioptric
Catadioptric scopes use a combination of a lens and mirrors. There are several main types, but the two most common designs are the Schmidt-Cassegrain (illustrated), and the Maksutov-Cassegrain.

Catadioptric telescopes mix the best qualities of refractors and reflectors.

Catadioptric scopes are suitable for use in terrestrial and astronomical viewing, show all types of objects well, and are especially useful for photography.

Apertures usually vary from 90mm (3.5″) to 406mm (16″ xxx). Most commercially made telescopes are 90mm (3.5″), 120mm (5″), 178mm (7″), 203mm (8″), 254mm (10″), 305mm (12″) and 406mm (16″).

Schmidt-Cassegrain (SC)
SC telescopes are the most common design of catadioptric telescope. Light enters the front lens, and is slightly focused towards the primary. The primary reflects the light to the secondary, which in turn sends it through the hole in the primary to the focuser, just like a Cassegrain (i.e. the only real difference is the use of a front lens).
The corrector (front lens) tends to receive special multi coatings that give it a distinctive colour (such as a deep purple on telescopes manufactured by Meade Instruments Corporation, one of the largest SC manufacturers in the world).

Maksutov-Cassegrain (MC)
MC telescopes are similar in principle to the SC design, but there are two substantial differences. MC telescopes use a different design of corrector: a concave lens that is specially coated and double sided. The mirrors are also curved strongly. The other difference is the use of internal baffles (shrouds around the secondary and a ribbed tube in front of the hole in the primary) that cut down on stray light and provide precision focusing. The big advantage of MC telescopes over other reflectors is that they are very accurate, and only very rarely require the optics to be collimated.

As has been already partially been explained, catadioptric scopes show virtually all objects (stars, planets, star clusters, galaxies, comets, nebulae etc.) well, and are perhaps the most solid all round design.
ACCESSORIES

First, a couple of definitions and an explanation:

Focal length (FL) is the length of the light path from the objective to the point where the image comes into focus. Different telescopes (or eyepieces) have different focal lengths.
For example, some refractors have a 700mm focal length and others 1000mm. Having a longer focal length usually means a longer telescope tube, but it also allows for higher magnification.

Focal ratio is the focal length divided by the aperture of the objective.
For example, a 700mm FL 60mm refractor has a focal ratio of f/11.6. The lower the focal ratio is, the greater the field of view will be. It will also be possible to take astronomical photos with shorter exposure time. Low focal ratios mean that a telescope is “fast”. However, lower focal ratio telescopes are more sensitive to accurate collimation.

Magnification is exactly that – magnification. Unlike binoculars, which (usually but not always) tend to have a fixed magnification, magnification in a telescope is highly variable, depending on what eyepieces are used. See eyepieces below.

Eyepieces
The most obvious and essential accessories for a telescope are eyepieces. Eyepieces come in a variety of focal lengths. Some come as little as 4mm (high power) or as large as 56mm (low power), where power refers to what kind of magnification you get.

As explained in the definition of focal length, telescopes with longer FLs can have higher magnification. For example, lets compare 700mm and 1000mm refractors.
A 700mm FL telescope with a 6mm eyepiece has a magnification of 116x (700mm FL / 6mm eyepiece). With a 56mm eyepiece, the magnification would be 12.5x.
A 1000mm FL telescope with a 6mm eyepiece has a magnification of 166x. With a 56mm eyepiece, the magnification is 17.8x.

Most telescopes come with at least one eyepiece if you buy commercially. However, it is best to build a collection of eyepieces to give you varying magnifications. Most of the time, you will actually use lower powered eyepieces if you live in the city, because of distorted seeing. Too much magnification can lead to a blurred image, and so is not necessarily a good thing (see the Misconceptions Page).

As well as eyepieces, you may want to investigate a barlow lens. A barlow is a device that effectively alters the power of eyepieces, so a 6mm eyepiece would effectively be a 3mm eyepiece if a 2x barlow is used. If we use the above examples, magnification would be 233x in the 700mm refractor, and 333x in the 1000mm. This example is a bit extreme, since most small refractors cannot resolve an image clearly above a magnification factor of about 50-60x per inch of aperture.
However, using the barlow with the 56mm eyepiece would give magnifications of 25x, and 35.6x respectively, which would deliver good views indeed.
One caveat about barlows: because they halve eyepiece FLs, it is possible to effectively wind up with two eyepieces the same. For example, If you have a 25mm eyepiece, and a 12.5mm eyepiece, putting a 2x barlow with the 25mm would be another 12.5mm eyepiece (25mm eyepiece / 2x barlow).

Eyepieces come in one of three common sizes (diameter of the barrel), to fit in different sizes of telescope focuser.

.965″ eyepieces are commonly designed for small refracting telescopes. However, the views are not as good as with 1.25″ diameter eyepieces, though they are cheaper.

1.25″ eyepieces are a common size on all types of telescope. They are a good compromise between price and performance.

2″ eyepieces are the most expensive, but potentially provide very wide fields of view.

Eyepieces themselves are generally one of several designs or sub designs, depending on their optical arrangements. Some use fewer elements of lens, some more. The three designs below are frequently used by astronomers, but are not the only types.
When considering eyepieces, you will need to consider two other things: eye relief (how far back from the eyepiece your eye will be when you can see the image filling up the eyepiece), and exit pupil (width of the light path from the eyepiece to your eye). For example, a 40mm eyepiece with 20mm eye relief and 5mm exit pupil means the eyepiece is designed for you to see the whole field of view when your eye is 20mm from the eyepiece, and the picture reaching your eye will be 5mm wide. Because everyone’s eyes are different, this information is best used as a guide when choosing eyepieces. People who wear glasses would be better off choosing eyepieces with a long eye relief.

Kellner eyepieces are generally the simplest, cheapest, and lowest quality design. Nevertheless, they are useful for astronomy on a budget, and lower powered eyepieces can provide good views.

Plössl eyepieces are what some would consider mid-range, but they also extended into the high end (quality) eyepiece range. They usually provide wider fields of view and a clearer image than Kellner eyepieces, but also cost more.

Othoscopic eyepieces offer fine images and have frequently been high end, with a price to match.

Motor drives
Motor drives can be placed on equatorial mounts to effectively drive the telescope for automatic tracking of an object across the sky. Most run off the mains, a car cigarette lighter, or batteries. On certain advanced telescopes however, such as the Meade LX200 (see the Going Further page), the standard altazimuth mount is motorized.

Filters
Filters are coloured attachments that are either used with an eyepiece or placed over the end of a telescope tube to block out different types of light. Different filters block different light wavelengths, and so have different applications. There are too many types of filter for me to explain here, but filters are commonly used when viewing nebulae (to block city lights / ambient light reflecting off the atmosphere, called light pollution), the Moon (to block out glare – it’s very bright), and for viewing the Sun (light is almost totally blocked. Don’t look at the porno through a telescope otherwise for obvious reasons!).

Photographic attachments
I will explain these more fully on the Photography Page. Telescopes can have film cameras attached to them via camera adapters. Most CCDs (Charged Coupled Device – see the Photography Page) can attach directly to the telescope focuser. There are also automatic guidance systems, which will also be explained.

Finder scopes and Telrads
Finder scopes are usually shipped with telescopes, but I mention them here because it is possible to get larger and better performance ones than are shipped with many telescopes. Finder scopes are small mini telescopes (of sorts) that are attached to the side of the real telescope. When searching for an object, it is better to use the smaller, lower powered finder scope to locate the object you want to view. It has a wider field of view than the main telescope (typically), and has crosshairs to help you centre the object.
Telrads perform a similar function to finder scopes, but work entirely differently. A Telrad is like a heads up display. It looks like a small TV screen of sorts, and projects a red (usually) bullseye onto the sky. The bullseye will be over the centre of the object you wish to view.

Erect image diagonals
When you look through a telescope such as a refractor, the image appears to be back to front. An erect image diagonal is designed to correct this problem giving an image that is oriented the right way around. This is important for land viewing, but less important for astronomy where there is no up or down, left or right.

Dew Shield
The last major accessory I want to deal with is a dew shield. While observing, dew builds up on telescope optics during cold nights. This causes fogging of the lenses, which can be detrimental if not removed (it can damage optical coatings and performance over the long term). The job of a dew shield is to help slow down the build up of dew, so you have more observing time before having to stop and save your scope. Dew shields fit over the front of the telescope tube assembly. Refractors generally come with them as part of the assembly, but they are extra items for other scopes.

SUMMARY
There is no “best” type of telescope per se. A lot of it is horses for courses. A large aperture telescope is best for all types of objects, but a small refractor is portable, simple, and good for planets, and casual deep sky work (don’t expect great images!).

Each of the three main kinds of telescope and their sub types have their own advantages and disadvantages. Ultimately, you might decide to build your own, which is the most cost effective option. Check with your local library or astro society for books and information on telescope making.

As always, try before you buy, if you decide to purchase. I waited for six months after getting into astronomy before I received my first telescope. I joined a club, started learning the sky, began using binoculars, then after evaluating my wish list and trying out several telescopes, I bought mine.

Despite there being no “best” telescope for beginners, there are appropriate choices. A small refractor is usually a good choice. I was thinking about buying a porno gratis myself, until I realized that if I got a bigger one, I would be able to see so much more, with what would be (for me) a lifetime investment.

So, after a good deal of thinking, I decided to go for my second choice: a 6″ Newtonian on a Dobsonian mount. While it is more expensive, I have found the views more than make up for the cost.