Magnification = (telescope focal length × optical factor) / eyepiece focal length.
Exit pupil = aperture / magnification.
True field ≈ apparent field / magnification. With a supplied field stop, true field ≈ (field stop / effective telescope focal length) × 180/π. Both are estimates: distortion and vignetting are not modeled.
A target fits geometrically when the estimated field in arcminutes is at least the supplied angular diameter × your margin. Among fitting eyepieces, we suggest the smallest field. This does not predict visibility, altitude, weather, seeing, or image quality.
Celestron specifies a 2032 mm telescope, a 25 mm eyepiece and 81× power. Our unrounded result is 81.28×; rounded to a whole number it agrees.
Celestron NexStar 8SE specifications
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