I’ve owned twelve Leica 50mm Summilux ASPH lenses in my lifetime, and three of them have been perfect in build quality and astoundingly sharp at f/1.4. The rest have been just short of exceptional. Most people wouldn’t notice… because they’ve never been crazy enough to buy, use, and sell multiple examples of them.
And don’t even ask me how many new Leica lenses will arrive with loose aperture rings, or wobbly built-in hoods, or back-focusing, or front-focusing, or… etc.
The moral of the story: in the case of Leica lenses, it can be advantageous to buy used vs. new in a sealed box. You not only save on price, you also have the opportunity to examine and photograph with the lens you’re interested in before purchasing.
—Peter.
Prosophos 
Hey Peter,
First off – glad that you’re posting again and whatever it is that caused your absence has been resolved happily.
Secondly, although I have not have not owned and sold as many 50s as you, I can say that I’ve had to fix my 50 f/1.4 as well and now it’s my 75mm that has focusing issues. On the other hand, a used 50mm summicron that I bought many years back is still perfect. As such, I concur with your comment.
All that being said, and despite the problems, I love the Leica lenses that I do have. I recently purchased the new 50mm apo summicron and I have to say that this is the absolute best yet. The price is crazy and I know I’m crazy for having unloaded my back account for it, but this lens is an absolute thing of beauty. I can’t seem to attach a picture for you to have a look-see so I’ll send it to you by email. It was taken at the CNE over the weekend. The shot has been cropped as I was some 30-50m away in the stands and it was shot wide open with a MM. Would love to hear your thoughts.
Cheers
Kevin
Hi Kevin, I had a look at the image and yes – the 50/2 apo and the MM are a phenomenal combination. No doubt about it.
Congratulations.
Amen.
Sums up my love-hate with Leica. I gave up on my purchase of a brand new 0.95/50 Noctilux when the first copy to arrive for my order back-focused. I waited a few weeks and the second copy arrived – sealed in box also – and was worse. My 1.4/50 LUX ASPH is perfect however, so it stays.
For a while I owned a 1/50 Noctilux. I picked it from a dealer here in HK after testing the four copies in his shop. I chose it on the basis that it was the only one to focus correctly at f/1.
All of which has made me a little more conservative. I find myself stopping down a little more now for ‘insurance’.