I have a 35 f3.5 Summaron with detachable goggles and the is an interlock which keeps the lens at infinity if you take the goggles off. Most wides designed for the M3 had the goggles held on with screws (wish I had a 35 f2.8 Summaron, with or without goggles). I have a 35 biogon for the Contax IIa which has no goggles but I use the Zeiss Stuttgart turret viewfinder .