The first 135 f/2 I bought was not good. The second one was much better - good wide open, very good at 2.8, but optimum at 4.0. I have to say that the 50 1.4 at 5.6 is sharper and the 200 1.8 wide open is sharper yet. Small differences, but differences nonetheless. The 135 f/2 degrades very little when stopped down further, staying extremely good to about f/11-1/2- f/16, after which is does suffer from diffraction limiting to a noticeable degree, while the 200 falls off sooner, becoming softer by f/11. All on a modified heavy duty Majestic with mirror up and cable, of course.