I have been using this unit for 4 years, only positive impressions. Nirazu did not let me down (3 times fie), in any weather: at minus 20, in drizzle, in the heat it works flawlessly. At the long end (370-400mm), for sharpness, it is advisable to cover a little hole, otherwise the picture turns out to be "soft": sometimes it is "to the face", sometimes you need to get sharpness. Pictures are clear and color reproduction is excellent. About HA, distortion, etc. I generally keep quiet - they are almost non-existent. In general, as befits L optics, the 100-400 is a great lens, though you have to pay for it . But still, 5 points.