Aperture is king. See how a telescope's resolving power, light grasp, and faintest visible star all follow from the diameter of its main mirror or lens.
Telescope OpticsLive
resolution · magnification · light grasp
Controls
Presets
Aperture rules everything: resolving power is θ = 1.22·λ/D (Rayleigh criterion), light-gathering scales as D², and the faintest visible star climbs with aperture. Magnification is just objective focal length divided by eyepiece focal length — and is useless beyond what the aperture can resolve.
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How it works
Resolving power follows the Rayleigh criterion θ = 1.22·λ/D, so larger apertures split closer double stars. Light-gathering grows as the square of the diameter, setting how faint a star you can see. Magnification is objective focal length divided by eyepiece focal length — but useful magnification is capped by what the aperture can resolve.
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