This will highlight what a rookie I am…But I recently bought a polarising lens having looked at one of my lens. I had assumed the lens size (and by that, I mean the glass area of the lens indicated by the arrow below…imagine I took the cap off!) was the same for each lens I had. This was a mistake!
But it really is quite simple. All you need to look for is the ‘o’ with a line through it, followed by a number. In the example above, it’s a 49mm lens.
See the area circled on the lens above. It’s has the symbol I mentioned followed by the lens size. It’s that simple. Wish I’d known that before ordering the filter…Oh well!