[vc13130]

My new Tamron 60 just arrived and I did some side-by-side tests between it and my old Nikon 60. I set both to infinity focus and compared the bokeh in pictures taken of a nearby object. I found that the Tamron showed the same bokeh at 2.0, 2.2, 2.5, and 2.8, BUT the Tamron at 2.2 still showed more out of focus regions than the Nikon at 2.8 did. That suggests to me that the Tamron is UNDERESTIMATING its speed--when the camera says it's at 2.8 it's really at 2.2 or 2.0. That explains why the PZ-tested sample showed such high MTF at "f/22"--the lens was actually at f/16 or f/13! That also explains why the lens underexposes more at "2.0" than at "2.8": at "2.8" the camera thinks it's 2.8 when it's actually 2.0 (sets speed X), while at "2.0" the camera thinks it's 2.0 and it is 2.0 (sets speed X/2, but the aperture is the same as it was at "2.8" when the camera set speed X, so you get underexposure).



I think the issue of CONSTANT underexposure is a different problem. My copy doesn't have it.



I don't have a tripod so my tests are not as quantitative as they could be. Also, I have to do some more tests to see whether this finding is consistent at other f-stops. But if this hypothesis is correct, then the lens is more or less redeemed. It CAN still be useful as a portrait lens! You just have to keep in mind that the aperture the camera reads is not the actual aperture, and maybe add some exposure compensation if your lens has that issue.