The one thing that bothered me a little bit about it when I played with a zm lens was that because you have the 1/3 stops, you DON'T have the half stops. I just found the half stops were easier and quicker to calculate in my head, so I missed them when they weren't there. Plus, I occasionally use my leica as a meter when I am shooting a meterless camera at the same time. Since I am very familiar with the leica's metering pattern, I can use it to accurately meter a scene and then transfer the same info to a meterless camera, be it a 4x5, or my M3...only having 1/3rd stop reading would add extra math....and I hate math. The lenses themselves are great though, and I am seriously considering possibly maybe taking a look at testing with the possible intent to rent to own the 21mm biogon.