As a lens cap - We now have two of them to choose from--15mm and 9mm fisheye. I think they're great. I have the original 15mm BCL and use it as a lens cap more than as a lens. It's tough to that though because lens caps are things I throw around in random pockets in my camera back and don't worry about scratching or whether or not it has a back cap on it. I got my BCL for $35 thinking it would be a bit banged up but nope, mint condition! So it's hard to "throw" it around, but that's what lens caps are for. As a backup wide lens - I usually walk around shooting with a relatively fast prime lens--30/2.8, 40/1.8, 50/1.7. I miss shots if these are too long but only take these lenses for creative photography so it isn't a big thing (if I were going to visit a famous building or something obviously I'd take a standard zoom). When I get tired of the manual focus, or when I want something wider, I throw on the BCL. If it's in my bag permanently like a body cap would be, I always have it. Focusing - Do you guys focus yours? Is it meant to be focused like that? On the 15mm you have to be like a meter or two away before 'infinity' is your best choice. Closeups, however, it pays to NOT use the 'macro' setting and focus by yourself just as you would a MF lens. It's much sharper this way and in the center at least, sharp enough for my needs (in other words, if I crop the middle 4MP to a 30mm it'd be considered a good lens!) 15mm vs 9mm fisheye? - I have the 15mm but kind of want the 9mm instead (or I guess I could say "as well" since the 15 isn't worth much to resell). The 9mm would be wayy different from whatever prime I'm carrying in my bag! Does anyone have both?