Standard eyepieces are relatively inexpensive designs which function very well. These include the types of eyepieces normally included with telescopes. The apparent field of view of a standard eyepiece is usually in the range of 40-50°. Early Eyepiece Designs The first telescope eyepieces, such as those used by Galileo, consisted of a single lens. (See the Understanding Eyepieces section for details on how eyepieces function in general.) Single-lens eyepieces suffer from a number of aberrations and provide only a narrow field of view. The first compound eyepiece, using two lens elements, was not developed until 1703, nearly 100 years after Galileo's first observations with a telescope. The eyepiece was invented by Christian Huygens, discoverer of Saturn's moon Titan (after whom the space probe which explored this moon three centuries later was named). Above: Optical diagram of a Huygens eyepiece A similar design was developed in 1783 by Ramsden. The Ramsden eyepiece is essentially a Huygens eyepiece with the bottom lens element reversed. This provided slightly improved image quality. Still, these eyepieces are limited in their usefulness on all but very long focal ratiotelescopes. Huygens and Ramsdens are still found today on inexpensive department-store-type telescopes. Improved Eyepiece Designs Simple eyepieces like Huygens and Ramsden designs suffer from chromatic aberration and narrow fields of view. In 1849, Kellner introduced the first achromatic eyepiece. It minimized chromatic aberrations and provided a relatively wide field of view. This design is still common on smaller telescopes for use at low magnifications. Above: Optical diagram of a Kellner eyepiece The orthoscopic eyepiece was invented by Abbe in 1880. "Orthos" are excellent quality eyepieces, providing high contrast and very good sharpness. They have short eye relief at short focal lengths (high power), making them somewhat difficult to use for planetary viewing for eyeglass-wearers. However, if eye relief is not a major issue, orthos make excellent planetary eyepieces. Above: Optical diagram of an orthoscopic eyepiece The most common eyepiece today, which is included with most telescope models, is the Plössl design. The Plössl was invented in 1860 but did not become a popular eyepiece until the second half of the 20th Century. Like orthos, Plössls have short eye relief, making them less well-suited to high-power viewing, although they have excellent image quality. Above: Optical diagram of a Plössl eyepiece Standard Eyepiece Prices Plössl eyepieces are among the most inexpensive designs. These types of eyepieces start around $30. Mid-range standard eyepieces cost about $50-60. Very high-quality eyepieces provide better contrast and improved sharpness, with higher quality coatings. These eyepieces usually cost around $100-150. Beyond Standard Eyepieces Advanced eyepiece designs improve on these types by providing a wider field of view or by providing longer eye relief. Wide field eyepieces are excellent for low-power deep-sky viewing, while long-eye-relief designs are good for planetary and other high-power observing. Other advanced designs include zoom eyepieces. These are discussed in their respective sections, linked from the Eyepieces page.