Optical telescope
Many types of telescope fold or divert the optical path with secondary or tertiary mirrors. These may be integral part of the optical design (Newtonian telescope, Cassegrain reflector or similar types), or may simply be used to place the eyepiece or detector at a more convenient position. Telescope designs may also use specially designed additional lenses or mirrors to improve image quality over a larger field of view. 
Design specifications relate to the characteristics of the telescope and how it performs optically. Several properties of the specifications may change with the equipment or accessories used with the telescope; such as Barlow lenses, star diagonals and eyepieces. These interchangeable accessories don't alter the specifications of the telescope, however they alter the way the telescopes properties function, typically magnification, apparent field of view and FOV.
Fremont Peak Observatory
The facility uses a telescope called Challenger. This is a 30-inch diameter telescope, "one of the largest telescopes available for public use" on an "English cross-axis equatorial mount" with a f/4.8 Newtonian lens. The telescope was made by Kevin and Denni Medlock from the Eastbay Astronomical Society, "in the early 1980s. First light was 1986." They "ground the mirror and built the scope in their garage". The scope weighs one ton and sits in a room the size of a classroom, according to intern, Edwin Levin, the "'mirror itself weighs 250 pounds. It's bolted into solid concrete, straight through the mountain, down to bedrock. A little motor, which matches the speed of the earth's rotation, keeps the telescope centered on the object we’re looking at.'"