(Description) Figure 3 Left: a typical pair of 10 × 50 binoculars. Right: comparison between the 50 mm objective lens of the binoculars and the 5 mm pupil of a typical eye. With ten times the diameter, the binocular lens has 100 times the area of the pupil, capturing 100 times as much light as the eye.

Week 2: Telescopes and visual observing

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Left: a typical pair of 10 × 50 binoculars. Right: comparison between the 50 mm objective lens of the binoculars and the 5 mm pupil of a typical eye. With ten times the diameter, the binocular lens has 100 times the area of the pupil, capturing 100 times as much light as the eye.