Why is aperture backwards??

 

New member
Username: Paulcarter698

Post Number: 1
Registered: Feb-21
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 - https://www.youtube.com/watch?v=fpdxMUWF0k0. 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???
 

Gold Member
Username: Magfan

USA

Post Number: 3634
Registered: Oct-07
Aperature is the number of DIAMETERS OF that number in the focal length of the lens.

So? An F2 lens with a focal length of 50mm (a normal lens for full frame and 35mm) will be about 25mm in diameter.

Each full stop represents 1/2 or double the preceeding stop. So? F2.8 admits 1/2 the amount of light as F2.0

If you do the math? Calculate SURFACE AREA and you'll quickly see the relationship.

You need to watch videos from people who actually know WTF they are talkng about.

Also? Look at shutter speeds. THEY TOO are 1/2 or 2x the one before or after. THIS makes it easy to calculate what is known as 'Equivalent exposure'.

1/60 at f2.8 is WHAT shutter speed at f5.6?
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