I found this lens as one of the best value for money. At still reasonable
weight you have long lens with very good F4 aperture. I did not make any
sophisticated tests comparisons but I found the lens sharp even when
fully opened, no vigneting and no noticeable distortions. Very good
contrast. I wanted to have the apperture ring so I could use this lens on
older body. I use it on FX camera bodies. Lens looks very robust and well
manufactured.