Eyepieces are available in various optical designs. Some manufacturers have exclusive rights to certain designs—such as Edmund Scientific's RKE models, Meade's Modified Achromats, and TeleVue's Nagler and Panoptic series. But the most common designs are sold by nearly every dealer.
Kellner, RKE, and Modified
Achromat eyepieces use three lens elements for good image quality at low cost.
A step up in quality and price are the four-element
Orthoscopic and Plossl models. Most manufacturers have matched sets of PlossIs in their catalogs—they represent the best buys in today's marketplace. Every telescope owner can use a set of three or four Plossls.
In the premium price bracket are eyepieces known by generic names such as
Erfles, and brand names such as Wide Fields, Ultra Wide
Angles, Panoplies, and
Naglers. These five- to eight-element models come in focal lengths from 35 to 4.7 mm.
Compared to a standard Plossi, these models all show a much wider field, providing a wonderful "picture-window" view of the universe.