Telescopes can have multiple uses depending on their design. Refractors and Cassegrains can provide a "correct-image" view, so they can be used for daytime land viewing as well as astronomy. Reflectors render the image upside down so they are not recommended for daytime viewing. This is not an issue for astronomy, however, because there's no "right-side up" in space.

The field of view expressed as part of a 360-degree circle. Holding your pinky finger out at arms length is approximately 1-deg wide. To convert this to the linear measurement of "feet at a thousand yards", multiply by 52.5. For example, at 1000 yards distance, a 7-deg binocular will see a width of 367.5 feet (7 x 52.5)

The distance, measured in millimeters, between the observer's eye and the eyepiece lens in which the entire field of view remains visible. Eye relief varies with the optical design but generally increases with decreasing magnification. Long eye relief is advantageous for observers who wear glasses, as they don't have to put their eye directly on the eyepiece to see the entire field of view, nor do they have to remove their eyewear.

The diameter of the circle of light exiting the telescope eyepiece. It appears as a distinct disk when the telescope is pointed at a bright source like the Moon. Also known as the Ramsden disk, the exit pupil varies with both aperture and magnification.