One of the most competitive segments in the amateur telescope marketplace these days spans 3- to 5-inch apochromatic ...

The triplet objectives are made with the same glass (both FCD 100 and FK-61) used in expensive refractors and are fully multicoated. The prisms are huge, allowing full coverage from any 1¼ ...

A phoropter is an instrument comprised of cylinders, prisms, and lenses that measures the eye’s refractive error to help determine and eye prescription. Phoroptors ...