Refractors work by bending — or refracting — the light that they gather to give you a view of your astronomical target. Easy to set up, the refractor is best suited to planetary and lunar viewing, making use of lenses to collect and focus light to form an image, while an eyepiece magnifies the view.
The refractor has a fairly straightforward design, with a main objective lens at one end and a star diagonal with a threaded eyepiece at the other. Being intuitive to use, the refractor is often a popular choice of instrument for novice astronomers given their low maintenance. Refractors are usually affixed to a simple alt-azimuth mount, that slews from side-to-side and up and down to locate a desired target. Being easy to use, means that these telescopes are also simple to manufacture (at least when it comes to the novice models) and therefore cheaper to buy.
The downside is that the higher the aperture, the more expensive the refractor gets. Unfortunately, this means that a basic refractor is also the number one target to replicate in mail-order catalogs and other non-reputable vendors so caution must be exercised when purchasing this type of telescope.
Refractors are particularly good at giving highly magnified and high contrast images and, because of this, are ideal instruments to use when looking at solar system targets such as the moon and the planets. The best refractors usually have an aperture of 2 inches (60mm) or more and will provide you with reasonable views of astronomical objects. If you're looking for a larger aperture, then a 3 to 4-inch (80 mm - 90 mm) would be best suited.
The drawback of a refractor is that it can suffer from chromatic aberration, also known as color fringing. When a single lens doesn't focus all of the colors emitted from a target object at the same point, bright objects such as the moon, Venus or Jupiter usually have a colored halo around them. To reduce this problem, many refractors are manufactured as achromatic or APOchromatic (also known as Extra Dispersion (ED) telescopes).
The achromatic refractor is cheaper than the apochromatic refractor and, combined with its efficiency, is often the type of telescope that novice astronomers go for. Even if you decide to go for the more expensive achromatic, you're still likely to get a stubborn degree of purple fringing around some targets.
Unless you're a seasoned skywatcher and you can afford to go for the more expensive apochromatic — which corrects for such an effect by using exotic glass for the lenses — this degree of color fringing will not ruin your observing experience to any great extent. If you do decide to go for the expensive option, then you will be stunned by the views you will get through these excellent telescopes. Be warned though, you might find that some apochromatics come without a tripod, something that you'll have to buy separately along with any accessories.