An eyepiece design consisting of three thick glass elements cemented together, with no air gaps, the outer two being of flint glass and the inner one of crown glass. The design, like other solid eyepieces such as the Tolles, is free from ghost reflections of bright objects in the field of view and gives bright images with good contrast. However, the field of view is rather small, about 30°, which makes such eyepieces suitable only for planetary and double-star observations. An adaptation is known as the Hastings triplet.
Subjects: Astronomy and Astrophysics.