The refractor telescope is the one most people picture when the think of telescopes– the eyepiece at the bottom end, the top end pointed to the heavens. It is also the design most commonly found at department stores. If you are interested enough in astronomy to be reading this article let it be emphasized here, avoid any telescope sold at any department store. You will most likely be buying into inferior optics placed on a substandard mount. This is not an indictment of refractors in general. Those sold by the several leading telescope manufacturers can generally be counted on for quality.

Before purchasing a refractor read this article and research other sources for the information you will need to make a decision you are happy with.

How the Refractor Works

The refractor uses lenses to collect and focus light. In its simplest form the telescope uses a convex objective lens to collect the light, which then focuses the light onto the eyepiece, the lens element which actually magnifies the image. As with any other telescope, the larger the objective, the more light is being collected and the more detail and resolution can be achieved. There are practical limits to how large the objective lens can be, however, and its disadvantages are the reason professional astronomy avoids the use of refractors. Here is a diagram of the major components of a refractor.

Following are the pluses and minuses of buying a refractor telescope.

Positive Features

• Optical elements maintain their quality well over long lengths of time.
• Closed system, resulting in less chance of moisture and foreign objects causing damage.
• No collimation necessary (realigning of optical elements).
• Usually easier to use, set up, and maintain.
• Achromatic refractor allows crisp image with medium size objective, higher f-number refractors and apochromatic refractors allow crisp, clear images in most refractors.
• Most of the light entering the telescope is saved from loss.

Negative Features

• Higher cost than reflectors for a given objective size.
• Chromatic and spherical aberration is inherent in the refractor design, and there is a high cost for correcting for it.
• Higher apertures require a longer focal length, requiring heavier mounts.

Michael Watson lives in Arlington, TX. His website is mikeslightbucket.com. Visit his telescope forum at mikeslightbucket.com Forum.