Test Your Birding Optics Knowledge

birding optics

Optics Question #1

When you see a binocular described as a 10×42 or an 8×30, the first number refers to the power or magnification. What does the second number refer to?
a) The weight of the binocular
b) The close-focus of the binocular.
c) The size of the front (objective) lens
d) The number of rotations of the focus wheel from close focus to infinity.

Answer: C. The second number is the diameter of the front (objective) lens, measured in millimeters.

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