zhangyue wrote: at f2.8, it clean up so fast that center performance close to f4... I see no visible improvement after f4
Thanks for sharing your observations. Well, you just confirmed what E. Puts had to say about this lens in his "Leica Compendium"
Similarly, I find it to perform the best between f/2.8-4. I used it at f/8 (LV+tripod) on D7000 and D800E and it does provide plenty of detail.
Yes, there are sharper 50mm lenses (Zeiss MP50) and lenses with more character (say, Nikkor 50/1.2 AIS) but overall Cron-R 50 is simply a great little lens and it's a joy to use. Price is a bonus as well!