Indeed, an excellent article Richard, also some comments are very interesting. BTW, I found a "Richard" in the comments (you?). Especially comment number 50 written by Michael Tapes (LensAlign), who includes a link by the way, is a point I want to draw attention to. Marc
PS. I have both SpyderLensCal and Michael Tapes' LensAlign. I ordered LensAlign after using LensCal once... and I've used LensAlign for all my lenses since then. LensCal = wasted money.