The refractor is the oldest form of telescope and was first used by Galileo in 1609. As explained above, it is a simple device with a lens for an objective which refracts the light down to a focal point. Refractors have one inherent problem in that the objective lens tends to act as a prism and split the light into its component colors. Thus the image you see may have color fringes on it. It is possible to correct this problem with compound lenses, and modern refractors are mostly free of this problem. However, a result of this correction is that the cost of the telescope is increased.
The refracting telescope is a good design which will out perform other telescopes of similar objective size. It is especially good for making lunar and planetary observations where resolving power is needed. The simple, unobstructed light path makes for a clear crisp image. However, refractors have some serious drawbacks, one of which is price. Those fancy, color corrected objectives are expensive. consequently, most instruments of this kind are four inches or less in diameter. Indeed, the refractor has the highest cost per inch of objective diameter of any amateur instrument. Another problem is that they do not gather much light. Most of them operate at around F 15 so that the image you see can be on the dim side. Therefore, they are not well suited for photography and for dim deep sky objects. However, for observation of bright objects such as planets, they are unsurpassed
