The optics of the telescope bear several similarities to those of the microscope. First, an objective lens is used to form an image of the object being viewed. An eyepiece is then introduced to view that image at increased magnification. As with the microscope, the total magnification of the telescope is a result of the individual magnifications of the objective lens and the eyepiece. The major difference between the two systems is that, while the microscope is used to view small (micro) objects and make them appear to be larger than they actually are, the telescope is used to view distant (tele) objects and make them appear closer to the viewer than they actually are. This chapter will cover the optical design considerations involved in the design of two telescope systems intended for distinctly different applications.
The astronomical telescope is distinguished by several unique characteristics. The magnification is generally quite high, with the upper limit being typically established by the resolution capability of the eye. The size of the objective lens is generally as large as practical, limited by budget and acceptable overall telescope size and weight. A series of eyepieces is generally part of the telescope package, allowing changes to overall magnification by exchanging the eyepiece being used.
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