> Contemporary photographic convention denotes lens apertures with a slash, such as ƒ/22 or ƒ/64, but in its writings the group always used a dot or period instead (as in "f.64").

Edit: then again at another point the article says:

> A small poster at the exhibition said:

>> Group ƒ/64 — >> >> ...

Either I'm misunderstanding something or the article is a bit confused.