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The eyepiece calculator reveals the observing potential of your telescope with Tele Vue Optics eyepieces. It accepts basic information about your telescope and displays results for all current Tele Vue eyepieces. Capable browsers can store and recall calculator runs. Refer to the diagram and tables below for the definition of the input and output parameters.Return to Results
apparent field: perceived span of sky seen through eyepiece
(without telescope). Not used in true field (see) calculation.
exit pupil: image of objective formed by eyepiece. Location where full apparent field is seen.
f/#: a ratio that describes the relation between the aperture and focal length of the telescope -- important for photography
field stop: ring inside the eyepiece barrel that limits true and apparent field size
focal length: effective distance from entrance of an optical system to focal point
magnification: relative change in angular size of object
true field: span of sky seen through telescope/eyepiece combination