Optical telescope
"Observable world" describes what can be seen using a telescope, when viewing an object or range the observer may use many different techniques. Understanding what can be viewed and how to view it depends on the field of view. Viewing an object at a size that fits entirely in the field of view is measured using the two telescope properties—focal length and aperture, with the inclusion of an ocular eyepiece with suitable focal length (or diameter). Comparing the observable world and the angular diameter of an object shows how much of the object we see. However, the relationship with the optical system may not result in high surface brightness. Celestial objects are often dim because of their vast distance, and detail may be limited by diffraction or unsuitable optical properties.
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.'"