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AINA 20 Inch Telescope Project
| Astronomy by the Letters (Dictionary)Apparent Field; The Angular size of the field determined by the eyepiece thru the field stop Aperture Gain; The proportional light gain of one objective to another. Take for example the eye versus an 8 inch telescope. The human eye has an aperture of approximately 7mm when dark adapted, an 8 inch telescope has approximately 200mm aperture 200/7=28.57 square that and you get 816.33, so an eight inch telescope gathers 816.33 times more light than the human eye. Dawes Limit; The smallest theoretical resolving power of a telescope. For example an 8 inch telescope 4.56/8=.57 arc seconds Exit Pupil; The image of the objective that is formed by the eyepiece. The size is determined by dividing the eyepiece focal length by the F# of the telescope. (as per the TeleVue Website) Field Stop; The metal ring inside an eyepiece that restricts the image size of the eyepiece. Focal Ratio; The ratio of the focal length to the aperture. An 8 inch scope with an 80 inch focal length equal 10 or a focal ratio of F/10 True Field; The true size of an image viewed thru the telescope in degrees. (Apparent field/magnification or field stop/telescope focal length x 57.3) |
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Copyright 2008 - Terry Pedroza |