Huygens Eyepiece
Christian Huygens developed the first compound eyepiece in 1703. A pair of plano-convex elements contain both spherical and chromatic aberrations. Long ago, Huygens eyepieces were standard equipment with telescopes of f/15 or greater telescopes. At the longer focal ratios, these eyepieces perform marginally well, although their field of view is very narrow. They lack an overall sharpness and are considered to have poor image quality.
Huygens eyepieces are generally the least costly eyepieces on the market. Huygens eyepieces incorporate two optical elements. They perform quite well on long focus refracting telescopes, but they can show image distortion as the telescope's focal length becomes shorter. Huygens are very good for projection of solar images since they don't use cement to hold the lens elements.
Ramsden Eyepiece
It was Christian Ramsden who invented this eyepiece in 1783. It is similar to a Huygens in that it consists of two plano-convex lenses, except both of the convex surfaces have identical focal lengths and they face each other. In most cases the lenses are separated by two-thirds to three-quarters of their common focal length, which represents a severe compromise between eye relief and aberrations. This design was an improvement, albeit a small one. in the history of eyepiece design.
Moderation Team
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