Sort of a simple question (I hope...) I have a 80mm lens for my Hasselblad 500C/M which features a B60 filter mount. I also have a B60-to-67mm conversion ring in case I can't find the filter I want in a B60 mount. My question is, when looking for closer focusing options, should I be looking for a B60 close-up filter, or would a 67mm filter be acceptable? This comes from the fact that I've been told that a close-up "filter" is really a diopter. I'm wondering if the diameter of the optical element would affect its characteristics. Thanks!