Telescope Tools & Calculators
The question every beginner asks is "what will I actually see?" These free, interactive calculators answer it from the physics — input an aperture and find out what it resolves, or match an eyepiece to your scope to get the real magnification and field of view. Each carries a "How this is calculated" note citing the optical formulas (Dawes limit, max useful magnification = 2× the aperture in millimetres, true field of view = apparent field ÷ magnification). No review claims — just the maths.
What Can I See? Aperture calculator
Enter an aperture in millimetres to see which planets, lunar detail and deep-sky objects it will resolve, its limiting magnitude, and its maximum useful magnification (the 2× aperture-mm rule).
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Magnification & true-FOV matcher
Enter your focal length, eyepiece and Barlow to get magnification, true field of view and exit pupil — and a flag when you are over-magnifying.
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