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Lecture 18 Optical Instruments

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  1. Lecture 18Optical Instruments Chapter 25 Outline • The Camera and the Eye • The Microscope and the Telescope

  2. Results from geometric optics Thin-lens equation Lateral Magnification 1 1 1  +  =  p q f  q M =  p For a system of two lenses, the image formed by the first one is treated as the object for the second one. The image formed by the second lens is the final image of the system. The overall magnification is the product of the magnifications of the individual lenses.

  3. The Camera The camera is a simple optical system to produce an image on film (we consider single-lens camera). Additional information about the light intensity (I) is needed. I is the rate at which energy is received by film per unit area of the image (A). I ~ D2, where D is the lens diameter A ~ q2, q  f A ~ f2 I ~ D2/f2 New parameter, f-number f/D  lens “speed”

  4. Diopter The power P of a lens in diopters equals the inverse of the focal length in meters: P = 1/f A converging lens of f = +1 m has P = +1 diopter. A diverging lens of f = 1 m has P =  1 diopter. If the far point of the eye is 25 cm (nearsightedness), a lens with f =  25 cm would correct the problem. The power of this lens is:  4 diopters (not  0.4!)

  5. Concept of Resolution Linear resolution is the minimum distance between any two objects to be viewed separately. Angular resolution is the minimum angle between any two objects to be viewed separately.

  6. Simple treatment of light as rays in the geometric optics approximation allows to design powerful optical systems (cameras, correction lenses, microscopes, and telescopes) Angular magnification describes an apparent increase of an object in size when a lens or a combination of lenses is used compared to the naked eye. Summary