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aperature number vs f number

Started 10 months ago | Questions thread
Dunlin Senior Member • Posts: 2,611
Re: Hang on.....

Len Philpot wrote:

f-stops are merely fractions. For example, f/8 means the aperture (opening) in the lens is 1/8 of its focal length. f/11 is 1/11 of the focal length, and so on. It's just a ratio.

That's why as the number gets larger, the opening -- and amount of passed light -- gets smaller. If you'll do the arithmetic you'll see that an aperture (circle) that's twice as large as another one will admit 4x the light. Conversely, an aperture half as large will admit 1/4 the light.

I didn't know that.

Thanks for the tip. 

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