Also known as a symmetric eyepiece, it is consists of two achromats. It offers long eye-relief and a superior field of view to the orthoscopic. It does fall short of the orthoscopic design with regard to distortion. Erfles usually consist of 5 or 6 elements. They offer a long eye-relief but relatively short working distance.
Distortion is comparable to the orthoscopic.
Designed at the impetus of the US Department of Defense and primarily for military use, GPS is now available to a variety of users worldwide. GPS receivers are used to locate your position anywhere on land or sea. Some advanced models will act as a lightweight handheld guide, reading your position, returning you to a fixed position, marking waypoints and setting courses to new locations. When choosing a laser pointer, price is not always the best criterion. All of our laser pointers are class IIIa laser diodes.