PIX 2015

What the heck is an f-stop?

Started Apr 25, 2014 | Discussions thread
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Re: What the heck is an f-stop?
In reply to Allan Olesen, Apr 26, 2014

Allan Olesen wrote:

D Cox wrote:

So the illuminance is directly proportional to the f number.

So if you change the f number with a factor of 2, you also change the illuminance with a factor of 2?

Or do you use an alternative definition of "directly proportional".

The illuminance is inversely proportional to the square of the f-number because it's proportional to the area of the aperture.

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