The "bird on a wire" picture above was the last shot I took with my Leica 90 f2. That the bird is slightly out of focus is actually why I don't own the lens anymore.
I loved the lens more than just about any lens I've ever owned, but it had a very strange focusing issue. It would focus just fine for a few shots, and then could not achieve focus at any f stop. The focus assist light indicated things were in focus but in reality wasn't even close. I shot literally hundreds of pictures trying to find something that would result in some sort of consistency and never did find it. I sent the lens to Don Goldberg at DAG and it similarly stumped him (he had me send it back for a second try, I even sent a K5 along so he could test it, but no success). I suspected my camera, except I had two K-1 cameras at the time and it behaved the same with both, plus every other lens I had (including Leica lenses) worked with the K-1. I consulted with David Llado at Leitax and he was stumped (and I tried two different adapters). I liked the lens so much I bought a second one, hoping I just had a bad lens. Nope, same exact behavior. If you read this thread from start to finish you will see other users struggling to focus this lens, doubting their camera, etc. Finally, after seeing a Chinese seller of Leica-Pentax adapters on Ebay exclude the R 90/2 I decided the most likely answer was that the R 90/2 only works inconsistently when adapted to K mount.
I had a brainstorm of trying the 90 Elmarit f2.8, but my first reading of its specs told me it had the same element/group arrangement (5/4) as the 90/2; I worried it would have the same problem. But a few weeks later I discovered the later version of the Elmarit has a 4.4 element/group construction so I gave it a try . . . and it works! I'm still testing it to see if it the same qualities as the Summicron (albeit 2/3 stop slower).
Update: I ended up returning this lens. It is a beautiful lens by any standard, but seemed to lack the magical glow of the Leica 90 Summicron. In fact, I spent time comparing it to my Voigtländer 90 f3.5 and liked the Voigtlander better despite being a bit slower. The CV was as sharp (sharper actually), a lot smaller, and rendered color virtually the same.
Test shot of fern in partial sun after adapting the Elmarit with a Leitax, @ f2.8:
Last edited by les3547; 10-19-2019 at 07:52 AM.