Just got a nice 500C/M (my first) with a WLF and I'm having the darndest time focusing the thing. I've had a Bronica SQ-A for a while now and find it easier to focus than the Hasselblad.
The 500's focusing screen has faint grid lines with a circular center area that looks like a microprism, but the prism-ness (for lack of a better word) of that area is almost imperceptible. Even with the magnifier I can barely tell when things are in focus. It's also rather dim.
I'm wondering if a newer screen would help. From what I've read, the Acute-matte D screens are supposed to be quite nice and much brighter. Also thinking that one with a microprism and split-screen would make things easier, but I'm worried about cluttering up the viewfinder. Will the Acute-Matte D screens fit the 500C/M?