How do I clean the external forward-facing glass on my lens?
Over the last year or so of use it has accumulated a little dust and a translucent smear mark. Nothing serious, but I'd like to remove them nevertheless. The lens in question is a Sigma AF 17-50mm f/2.8 EX DC HSM OS and has a flat external forward-facing glass element (e.g. see here).
I've never cleaned any camera equipment before, so pitch this to a novice audience please.