55mm I think. Yes I did exchange the vitacon, but I do not have the attachment nor the step up ring. Very sad to say, I was exhorbitantly overcharged for the lens so I will not go into details. I will definitely not go back to the shop. I believe, last I heard, you may be able to get the C-180 lens at $70 at Mustafa. Anyone who wants to know what happened may pm me.