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Sep23-10, 01:55 PM
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