dna86 wrote:
Yes, I do know why the aperture numbers are a sqrt(2). It has to do with cameras being two dimensional and light falloff with the square of the distance. If yoiu double the distance from a light, the light drops by 1/4. If you move the sqrt(2) away, then the light halves.
Nope. It has nothing to do with distance to the subject. It wasn\'t supposed to be a trick question.
A full-stop change in aperture, shutter speed or ISO causes either twice the amount of light to illuminate the sensor/film, or half the amount of light. This is equal to +1 Exposure Value (EV) or -1 EV. You get a +1 EV increase at the sensor/film plane by either: (i) doubling the area of the aperture opening; (ii) doubling the amount of time the shutter is open; or, (iii) doubling the ISO or sensitivity of the sensor/film. Since aperture f-stop is defined as a ratio of diameters*, and doubling the aperture area corresponds to increasing the aperture diameter by a factor of sqrt(2), the ratio of adjacent f-stops (or 1 full-stop changes) is sqrt(2) = approx. 1.4.
* f-stop = diameter of lens front element divided by apparent diameter of aperture opening, as seen through the front element.
Nov 03, 2009 at 09:10 AM
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