I have a Rollei 3.5T, which I have put some money into, and works fine. It uses Bay 1 filters, etc, I'm told. I have all the color filters I need in 52mm Nikkor filters. Is there an adaptor ring I could get to use these filters on the Rollei (ie from Bay 1 to 52mm thread)? I would accept the obstruction in the viewing lens.
I own an adapter between Bay 1 and 49mm and know that those adapters are not uncommon. Maybe there is Bay 1 to 52mm, but if you cant find one you can buy B1/49mm and use step-up ring to 52mm. Look on eBay.
Purpose built adaptors may be difficult to find. What I have done was to break the glass of a tatty Bay1 filter and glued it to 34-37 step-up ring. From then on all will become easy. Funny enough, I have found a Bay2 - 49mm and a Bay2 - 52mm easily.