This lens is one of the least expensive Sonnar formula lenses that you can buy for the Leica, the slower Jupiter-8 is even less. I like the F1.5 speed of the Jupiter-3, and the lens is a favorite of mine. The reputation of this lens was so bad that i bought 4 of them to find out why. With a little work, basically setting the Shim of the lens to optimize for the Leica, found it to be as good as My Nikkor 5cm F1.4. Many lenses later, this one is made from a 1955 KMZ Jupiter-3 with a front element replaced using a 1983 lens, and the optics module set in a newer black mount. It's been on my M8 since making it two months ago. Wide-open at F1.5, today, on the M8, ISO 160.