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Natural viewpoint/ Focal length of human eye ?

Chas Tennis •

Contributing Member

• Posts: 912

Estimate using thin lens formula, 1/s + 1/s’ = 1/f


1

Let’s say that an eye ball is 1″ in diameter. Relaxed, the internal eye lens of the normal eye has the shape to focus at infinity. Therefore, the focal length of the
entire
eyes, that is, cornea lens + ‘eye lens’ is 1″. [The cornea is a fixed exterior lens component of the eye, also the eye has the internal ‘eye lens’ that changes shape.]

The normal eye can
accommodate, or change its shape & focal length to read comfortably at 16″. Let’s estimate that the closest focus limit is 12″ for a healthy eye of a young person.

Estimate focal length necessary for the 1″ diameter eyeball to focus at 12″ using the thin lens formula

1/s + 1/s’ = 1/f

s = image distance 1″, s” = object distance 12″, f = focal length

f = 0.92″

(Is 12″ a good estimate for closest focus? See how close you can focus but not in very strong light. The eye iris will go to a small aperture in bright light. If the diameter of the iris is small the focus might appear to be closer than if the eye were using more of its aperture. Similar to the principle of a pinhole camera.)

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Chas Tennis

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Sumber: https://www.dpreview.com/forums/post/53520393

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