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Sep23-10, 01:55 PM
berkeman's Avatar
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Quote Quote by Peter Watkins View Post
Visual information arrives via photons of visible light. These, we are assured, all travel at the same speed and therefore have the same impact. Why then, do those that travel a little further require a change in the shape of the receiving lens? In particular, nearby objects at distances of, say, 3 feet and 6 feet, require a considerable change of focus. This cannot be due to binocular vision as monocular vision also has to be focused.
It's just basic optics. See the Lens Equation part-way down this page:

1/S1 + 1/S2 = 1/f