What would it be? This thread was suggested on another thread asking which lens you have but don't use. At heart, I am somewhat of a minimalist, but looking in my camera bag might suggest otherwise. Admittedly, I always sense 'diminishing returns' as regards pleasure in a hobby the more I purchase. One lens is good...are five lenses 5 times better? My bag includes the 23/2, Zeiss 32/1.8, 50/2, 18-135, and 5 or 6 adapted lenses. A modest set up, to be sure. So which one would I keep if a law were passed restricting us to one lens? I can't really say. It would not be a zoom. Preferably, a prime between 16 and 50, and capable of reasonably close focus. When I was younger, I pursued subjects. Now, I'd rather they come to me. Not out of laziness, but perhaps the discovery there are a lot of normal, everyday things to photograph out there, and the normal can become interesting through a lens. Maybe the lens determines for me which one of those I choose to shoot. So give me a prime...under 50mm. Anyone else?