an eyepiece for a telescope designed for visual observation of the sun. A solar eyepiece is used to provide a reduction in the brightness of the sun’s image with minimum loss of the telescope’s resolving power. By contrast, when the lens or mirror that produces the image is stopped down with a diaphragm for this purpose, the resolving power of the telescope is diminished. Devices used in solar eyepieces to attenuate the light include neutral filters, photometer wedges, and polarizing devices.
In the most common type of solar eyepiece, the light is reflected from the plane mirror or wedge M (see Figure 1) and then passes through a two-component prism. The prism Pj is made of crown glass, and the prism P2 is a liquid prism filled with liquid petrolatum. Since the refractive indexes of the materials of which the prisms are made are very close in value, only a small portion of the light is reflected from the interface. This light then passes through the ordinary ocular O.