If you get across from Melbourne to Tassie at some stage for a visit, let me know, and I'll give you a try of a Rollei or a Mamiya, you'll enjoy it, I'm sure. But it can be addictive. 😉
Yes, you can indeed stop a 2.8 down to 3.5; but the lenses are 80mm versus 75mm respectively for the 2.8 & 3.5 models. And various lenses were used, from 80mm f/2.8 four element Tessars (rare) to 75mm f/3.5 four element Zeiss Tessars and Schneider Xenars, through to five and six element versions of the 75mm Schneider Xenotar and Zeiss Planar. All these in addition to the five element 80mm Xenotar and Planars, which had their elements arranged slightly differently. Not to overlook the quite rare Zeiss Jena 80mm f/2.8 Biometar as well. So there is a bit more too it than which aperture size, although I should say I think too much is made of these differences. And of course as Brian says there are weight and other differences such as light meters, for instance, from model to model. But Robert Doisneau, for example, was limited to a humble 75mm Tessar back in the 1930s, and yet it didn't seem to do his images much harm from what I've seen of them. Any of them are likely to be better than 99% of their owners and I certainly don't include myself in the 1%.
Regards
Brett
