I have an older Hasselblad (500C). I like using the viewfinder with this camera, but I have a few questions. Is the correction lens user replaceable? It has a bit of haze which I can't seem to get rid of. If not, I'll get another viewfinder instead. Are the newer ones (say, for the 501 cm) different (bigger diopter or better made) and would they fit the older cameras?