In looking for close up lenses for a Bessa II, I happened upon the Zeiss Opton Proxars in the A37 size. Actually I bought two of them, a f=1m and a f=2m, which I'm assuming will work on the Voigtlander. The question is are they the same strength as the Focar and can they be used interchangeably as if they were a Focar. Thanks, Bill Barber