This is a quick note which will be of interest to almost nobody, except perhaps the person who asked about it on Flickr, but whatever, I’m in a public service kind of mood.
A while ago I invested in the Lee RF75 filter system, which fits nicely on both my Hasselblad XPan and Olympus micro four thirds lenses. My source for this kind of equipment is the ever reliable Robert White.
“The RF75 will take 2 filters as standard and can be adjusted to take a single filter to enable its safe use on the widest angle lenses, like a 30mm on the Hasselblad XPan.”
However, I’ve found to my cost that this is not 100% accurate, at least not when using the RF75 clip-on polariser. Skipping the point that using a polariser on a ultra wide angle lens is not always a good idea - at least not if you’re using it for the basic make-the-sky-prettier application - unfortunately it is not safe on the XPan 30mm lens.
The examples below are straight uncorrected scans direct to JPG.
Evidence, case 1. The “blue sky” test.
Evidence, case 2, Vegetation, reflections test - something you might conceivably want to do even at 30mm.
So, in conclusion, the RF75 polariser can be used on the XPan 30mm, but you need to remove all but one filter slot, and be very careful. And take a safety shot without it on.
This is really an extreme case, and is in no way a criticism of either the Lee RF75 (or the similar “7” system) or of the Robert White team. They’re both excellent.
p.s. - there is no issue using the polariser on either the 45mm or 90mm lens, or indeed any Olympus lenses I’ve tried it on. This, I repeat, is an extreme case.