2303_-_Spr_2011_-_Week_7_-_Geometrical_Optics_-C

# 2303_-_Spr_2011_-_Week_7_-_Geometrical_Optics_-C - LENSES 1...

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1 1 LENSES

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2 2 Week 7.1 - Homework Review Lenses The Lensmaker’s formula Summary of lenses and mirrors Chapter 36 nikon fisheye lens
3 3 A lens is used to image an object on a screen. The bottom half of the lens is covered. How does the image change? (a) bottom half of image disappears (b) top half of image disappears (c) entire image reduced in intensity Cover ½ Lens

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4 4 Half of the rays are blocked, so the intensity is reduced but the image is of the entire object Cover ½ Lens
5 5 Divergent lens For a divergent lens, f < 0

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i 6 6 Divergent lens Ray tracing for a divergent lens , f < 0
7 7 The image on the back of your retina is a) enlarged b) reduced The image on the back of your retina is a) real b) virtual The image on the back of your retina is a) inverted b) noninverted The lens in your eye a) is always a positive (i.e., converging) lens b) is always a negative (i.e., diverging) lens c) is sometimes positive, and sometimes negative, depending on whether you are looking at an object near or far away d) is positive if you are near-sighted and negative if you are far-sighted UIUC

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8 8 The Lensmaker’s How do you make a lens with focal length f ? Start with Snell’s Law. Consider a thin plano- convex lens: R n air h θ light ray n air=1.0 Snell’s Law at the convex surface: Assuming small angles, The bend-angle β is just given by: UIUC
9 9 The angle θ can be written in terms of R , the radius of curvature of the lens : The bend-angle β also defines the focal length f : So, R N air h light ray ( N air=1. 0) The Lensmaker’s Formula UIUC

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10 1 Some Simple For Lens-maker’s Formula, R > 0 if convex when light ray hits it. Double convex R1 > 0, R2 < 0 Double concave R1 < 0, R2 > 0 Plano-convex R1 = ∞, R2 < 0 EG
11 1 Lensmaker’s Formula The thin lens equation for a lens with two curved sides: R1 > 0, R2 < 0 UIUC

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Week 7.2 Quiz
13 1 Fiber Optic Cable Wikipedia For step index fiber, a typical value for the ncladding = 1.46, ncore = 1.48.

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## 2303_-_Spr_2011_-_Week_7_-_Geometrical_Optics_-C - LENSES 1...

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