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Why is aperture backwards??


So, I get that larger f numbers like f/22 actually mean that it's a smaller opening and that smaller f number like f/2 is a big opening. I learned that thanks to a really helpful beginner video I just watched - this video. But my question is this...WHY is the size of the aperture backwards from the numbers. Shouldn't f/22 be a big aperture since it's a big number and f/2 should be a small aperture since it's a small number???
Cephus 16 2.6k England
26 Feb 2021 9:40AM
Suppose we have a 50mm focal length lens. If we have a big size hole – a big aperture, it might measure 25mm. So 50 divided by 25 gives us 2: the f/number is 2, which we write as f/2.

If the aperture is smaller, say, 3mm in diameter, 50 divided by 3 gives us about 16: the f/number reads f/16. As the hole is smaller, less light gets through. So f/16 is said to be a small aperture or small f/number.

That’s why you could get confused if you read about an aperture of 16 being smaller than 2: that does not make sense and is, in fact, wrong. A photographic aperture is written as ‘f/number’: it means the focal length divided by the aperture diameter. So f/16 is indeed smaller than f/2

Google is my Friend. WinkWinkWink
mervyntattoo 11 945 Wales
26 Feb 2021 10:22AM
Think of it as a resistance like in an electric circuit.
rambler Plus
12 1.0k 17 England
26 Feb 2021 11:34AM
I like to of it by thinking the small f numbers give a narrow depth of field or focus, or large f numbers a large depth of field

Ken
mrswoolybill Plus
14 2.7k 2397 United Kingdom
26 Feb 2021 11:52AM
As Cephus says - the F/ number is the focal length divided by the diameter of the aperture. For this reason a particular F number does not indicate a fixed size of aperture, the size varies according to the lens.
thewilliam2 4 1.5k United Kingdom
26 Feb 2021 2:29PM
The F stop doesn't actually tell us how much light will reach the film or sensor, which is why the movie world uses T stops, where the f stop has been corrected to transmission losses.
pablophotographer 9 1.8k 405
26 Feb 2021 7:12PM
F denotes a fraction calculation.
The larger the denominator the smaller the result of the division, thus smaller the iris hole.
Big Bri 19 16.7k United Kingdom
27 Feb 2021 10:50AM
As they said ^

In other words, 1/2 is larger than 1/4

thewilliam2 4 1.5k United Kingdom
27 Feb 2021 1:17PM

Quote:As they said ^

In other words, 1/2 is larger than 1/4




Those of us who have done any teaching will know that some students don't readily accept that fact and are only convinced by a demo of cake-cutting!
27 Feb 2021 4:06PM
Reminded me of a brilliant illustration of that fact 'thewilliam2' I was trying to get a class to understand measuring and was using the illustration of 'hands. So I asked them to stretch their fingers out amd make a mark where the tip of their little finger came and where the tip of their thumb came and then to measure it with their rulers. I then asked them to get the measurement of two hands, which they did. But when I asked what the measurement of three hands would be there was silence until a little voice piped up 'I haven't got three hands miss'.
Thank you so much
"WOW, so many responses! You guys are awesome, I will review your responses when I get home today!"

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