ch24notes - ∞ “Prescription Principle:” Corrective...

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Chapter 24 Notes College Physics by Giambattista et al. John B. Ross, Ph.D. IUPUI Physics Dept. Lenses in Combination 1) The image of the 1 st lens (“objective”) is the object of the 2 nd lens (“eyepiece”). 2) m total = m 1 ·m 2 The Human Eye retina ciliary muscles Image formed at back of retina cornea (about 2.5 cm behind lens) lens optic nerve Cornea – responsible for large bending of light, “coarse adjustment” Lens – focuses ( accommodates ) close and distant objects, “fine adjustment” Ciliary muscles – change the focal length (curvature) of the lens to accommodate close objects. Greater muscle power for closer objects. f must be adjusted to accommodate different object distances since the image distance is fixed (2.5 cm.) Near Point ( NP ) – closest point that may be seen in focus (normal = 25 cm). Far Point ( FP ) – farthest point that may be seen in focus (normal =
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Unformatted text preview: ∞). “Prescription Principle:” Corrective lenses create images of objects outside of the range of clear sight and place those images within the range of clear sight. Refractive Power meters in f P 1 unit: diopters (D) Nearsightedness (Myopia) : Far Point < ∞ Eyeball too long treat as if lens is too powerful, so use concave lens to correct. Prescription: f = – FP Chapter 24 Notes College Physics by Giambattista et al. John B. Ross, Ph.D. IUPUI Physics Dept. Farsightedness (Hyperopia/Presbyopia) : Near Point > 25 cm (Hyperopia) Eyeball too short treat as if lens is too weak, so use convex lens to correct. (Presbyopia) ciliary muscles too weak to accommodate close objects. f NP cm 1 1 25 1 Prescription: 25 25 NP NP f...
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