Spring 2012

Spring 2012
by ani

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F-number equals the focal length of the lens divided by the diameter of the entrance pupil. Since both measurements are linear dimensions when the same units of measurement are used for both the focal length and the diameter of the entrance pupil then they cancel each other out without any further conversion. If the measurement units are dissimilar then ...


Sensor dimensions don't matter. F-stop is shorthand for "fractional" and what it's a fraction of is the lens focal length and the diameter of the iris and the real calculation is simply the lens focal length / diameter. 50mm lens with an iris 25mm across is at F2. So in your case, if you know the Radius then it's simply FStop = FocalLength / (Radius * 2)


Due to diffraction, and aperture size, F8 on a compact camera is equal to f22 on full frame, and F2 on compacts is equal to f5.6 full frame , and that's why f2 (F5.6) doesn't give the same background blur as F2 full frame. Therefore Sunny 16 rule for compact cameras is sunny 5.6 rule- so instead of 1/100th at F16 ISI 100, you would have 1/800th at F5.6 F8 =...


This and all similar questions are best answered by looking at websites designed for the purpose. One approach is to look at vendors like B&H Photo, which offers convenient filtering. For example, Canon EOS EF or EF-S lenses classified as "wide" or "wide zoom" with an aperture of f/1.4. Or, use a website dedicated to the task, like the Neocamera database....

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