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[1] [2] [3] The f-number is also known as the focal ratio, f-ratio, or f-stop, and it is key in determining the depth of field, diffraction, and exposure of a photograph. [4] The f-number is dimensionless and is usually expressed using a lower-case hooked f with the format f / N , where N is the f-number.
The focal ratio of a telescope is defined as the focal length of an objective divided by its diameter or by the diameter of an aperture stop in the system. The focal length controls the field of view of the instrument and the scale of the image that is presented at the focal plane to an eyepiece , film plate, or CCD .
The fast focal ratio of f/2.4 and large image sensor result in a relatively large field of view, with each GOTO system having a total FoV of approximately 40 square degrees, [2] around 200x the area of the full Moon in the sky. The fast focal ratio also means that only a small amount of time is needed to observe each area of the sky, with each ...
Considerably higher magnifications can be reached with this design, but, like the Galilean telescope, it still uses simple single element objective lens so needs to have a very high focal ratio to reduce aberrations [13] (Johannes Hevelius built an unwieldy f/225 telescope with a 200-millimetre (8 in) objective and a 46-metre (150 ft) focal ...
The small telescope has an aperture of 50 mm (2.0 in) and a relatively long focal length of 500 mm, for a focal ratio of f/10. [2] Design and configurations At the ...
Each Unit Telescope is a Ritchey-Chretien Cassegrain telescope with a 22-tonne 8.2-metre Zerodur primary mirror of 14.4-metre focal length, and a 1.1-metre lightweight beryllium secondary mirror.
The ARO 12m Radio Telescope (ARO12m or KP12m) is a 12-meter dish located on Kitt Peak, ... Focal Ratio (f/D) Prime = 0.4, Cassegrain = 8.0 Surface Accuracy
UH88 is a Cassegrain reflector tube telescope with an f/10 focal ratio, supported by a large open fork equatorial mount. It was the last telescope on Mauna Kea to use a tube design rather than an open truss, and is the largest in the complex to use an open fork mount, with neighboring telescopes in the 3-meter class using English mount designs.