Thread: Choosing an ISA
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Old Aug 20, 2009, 9:25 PM   #9
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Originally Posted by Africa View Post

What is probably confusing you is the f-stop. The f-stop is a number that represents the aperture opening. This is a list of f-stops commonly found on older film camera lenses.
f 1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16, 22.
The higher the number the smaller the opening. Why?, because the number is actually a fraction, therefore f16 would be 1/16, a smaller opening than f4, or 1/4.

I have found that it is less confusing to newcomers if one uses the correct way of expressing aperture, which would be f/1.4, f/2, ..... f/22. Explain that it is written that way because the number is the result of the focal length divided by the actual aperture. I.E. - 50mm focal length lens with an actual (effective) 25mm diameter aperture is f/2.

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