While going through manuals of the various Bronica S2/EC/EC-TL models I discovered there has been a HC-NIKKOR 75mm/2.8 lens. I was unable to find anything else about it; I have a PC-NIKKOR 75/2.8, what would be the practical difference of these lenses? I realize the H in HC stands for 6 elements, so maybe it's planar-style lens instead of the 5-element design of the PC-NIKKOR. But is it in some way better then? Any other differences, like filter thread size etc.?