This is an exceptionally superb Leica zoom lens and the quality is as good as a Leica Prime lens of any focal length. The optical performance compared to other zooms of the same length is beyond comparison. The snag is that it weighs almost 2 kgs. It is best used on a tripod or with a camera shoulder stock ( as shown in pic ). The optical performance at full aperture is brilliant and the optimal performance is at f4. There is a slight fall off till f8.
I used this lens with the DMR in Pacu Jawi last year.
I am going to the next Pacu Jawi. But, I am going to use this lens with Canon 5D Mk2.