PHYS 131 Lecture Notes - Lecture 12: Shutter Speed, Sclera, Dioptre
14 Nov 2017
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Document Summary
We can control how much light enters the camera via a diaphragm (stop) The size of the opening (iris size) is defined by the f-number. We write this is as f/n, where n is the number: N=focal length of lens/ diameter of iris. The larger the effective diameter of the lens, the smaller (shallower) the depth of field. Objects in focus only over a small range of distances f/8 f/5. 6 f/2. 8. Brightness of images vs area of the lens: Lens has a circular shape, so its area = r2 where r is the radius of the lens. Amount of light energy per second entering camera depends on area of the lens. R is half the diameter (d), so: area = (d/2)2 d2, area d2, d area. In photography, f-numbers are arranged in order of doubling the intensity of light getting through the camera. This is achieved by doubling the area: light intensity on film (iris diameter)2.
