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p2020chap14

# p2020chap14 - PHYS-2020 General Physics II Course Lecture...

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Unformatted text preview: PHYS-2020: General Physics II Course Lecture Notes Section XIV Dr. Donald G. Luttermoser East Tennessee State University Edition 3.3 Abstract These class notes are designed for use of the instructor and students of the course PHYS-2020: General Physics II taught by Dr. Donald Luttermoser at East Tennessee State University. These notes make reference to the College Physics, 9th Edition (2012) textbook by Serway and Vuille. XIV. Optical Instruments A. Common Optical Tools. 1. A camera consists of a lens (or series of lenses) that focus an image onto a light sensing detector ( e.g. , film, CCD, etc.). a) The diameter of the lens can be stopped-down to smaller sizes by adjusting the aperture opening. i) These stops are technically referred to as the f-number . f-number ≡ f D (XIV-1) f = focal length of lens. D = diameter of the lens or aperture (whichever is smaller) ii) The larger the f number, the less light is allowed into the camera. iii) Cameras typically have the following f-stops: f /2.8 (lets the most light in), f /4, f /5.6, f /8, f /11, f /16 (lets the least amount of light in). b) The magnification of the image follows the thin lens for- mulae ( e.g. , Eq. XII-10) with an image size given by h prime = h p f . (XIV-2) c) The amount of light that falls on the detector is deter- mined by the f-stop and the shutter speed. i) For fast moving objects, one should use shutter speeds 1/1000th or 1/500th of a second. XIV–1 XIV–2 PHYS-2020: General Physics II ii) For indoor, low-light levels, speeds greater than 1/60th of a second are required = ⇒ speeds longer than 1/60 sec usually require the camera to be mounted on a tripod to keep the camera steady. iii) Astronomical photographs typically require the shutter to be open from minutes to hours in order to record the image. 2. The organic analogy to the camera is the eye . In the case of the human eye we have the following characteristics: a) The iris is equivalent to the aperture of the camera = ⇒ the opening is called the pupil . b) The cornea is a transparent lens cap for the eye’s lens . c) The retina records the image and sends the signal to the brain via the optic nerve = ⇒ analogous to the film in a camera or a CCD chip. The retina is composed of 2 types of receptor cells: i) Rods are able to detect low light levels in black- and-white. ii) Cones come in 3 types that respond respectively to red, green, and blue light....
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p2020chap14 - PHYS-2020 General Physics II Course Lecture...

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