Eye piece or ocular lens is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. This optical instrument is named so because it is usually the lens that is closest to the eye when someone looks through the device. In this, objective lens or mirror collects light and brings it to focus creating an image. The eye piece consists of several "lens elements" in housing, with a "barrel" on one end. Different eyepieces vary in size, focal length and design as per the application. The simple designs give acceptable performance and in some cases even phenomenal performance.