Get L-mount system at B&H Photo.
My review of the Leica 90mm f/2 APO-Summicron-SL ASPH and Leica 75mm f/2 APO-Summicron-SL ASPH were severely impacted by a problem which I document in this analysis. It was very confusing, and cost me irreplaceable time and effort to diagnose, damaging hundreds of my images and forcing me to shoot and reshoot with the same crappy results until I worked out an imperfect work-around. I first noted the issue in Leica 90mm f/2 APO-Summicron-SL Aperture Series: Mosaic, Focus Shift.
Anyone using Leica SL lenses would be well advised to read this piece. I offer an imperfect work around prone to repeated sub-optimal results in some conditions, though usually successful. The same issue applies to the Leica 75mm f/2 APO-Summicron-SL ASPH and I will soon publish a similar series showing that. I suspect that it affects all or at least most Leica SL lenses.
Below, two frames at f/2. The lens focus was not changed by me. I can reproduce this behavior at will.