Why is the F-stop scale so weird?

Shutter speeds are pretty easy to understand — but why do apertures increase so weirdly? How come bigger numbers are smaller apertures? And how the hell are you meant to remember all of this?

Why does it matter?

ISO and Shutter speeds

Before we dive into aperture-land, let’s take a look at shutter speeds. As I hinted at before, they are both pretty intuitive: A 2 second shutter speed means that the shutter is open twice as long as a 1 second shutter speed. The same goes for 1/100 and 1/200 — the former is half as fast as the latter.

The scale of F-stops is a geometric sequence of numbers: the sequence of the powers of the square root of 2.

F-stops and aperture

A lens, fully stopped down. Look how dusty it is, though! Ugh.

The F-stop scale

Where do variable aperture lenses fit in?

You may have seen some lenses that have something like “18–35mm f/3.5–4.5” stamped on the side of them. That means that when the lens is zoomed out fully, you can shoot with a f/3.5 aperture. However, when you zoom in, you can only use f/4.5.



Amazing things you always wanted to know about photography — but was too scared to ask!

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