First of all my copy of the Sonnar 5,8cm f/1,5 has some strange sharpness issue. At the point where it should be in focus it becomes unsharp. I have never seen such kind of thing. When you focus from infinity to in-focus you notice that you are almost there and then it becomes unsharp and then it gets sharper again just to become unsharp because you are now leaving the in-focus area. This is most noticable wide open. But even at f/2 it is quite soft when in focus. This makes it hard to focus even or especially using a mirrorless camera and when zoomed in to a high level.
I tried to visualize this effect. I compared my Sonnar 5,8cm f/1,5 with a wartime LTM Sonnar 5cm f/1,5 and a post-war Biotar 5,8cm f/2.

For this test I stood in front of a large black and white picture and did 5 images at 5 different focus positions. From totally out of focus the lens focused on far away to in-focus and then to totally out-of focus focused very close.
a -> lens focused almost to infinity, b -> focus almost achieved, c -> in focus, d -> focused closer than in focus, e -> lens focused very close
You can clearly see that at point c (the in-focus point) the Sonnar 5,8cm is visibly softer than the focused before and after this focus point. Believe me this is no shake or misfocus. The out-of-focus area on the close side looks suspicious too. Does anyone have an explanation? Is my copy faulty?
I did some comparison shots with those 3 lenses yesterday. Here is one set.
Sonnar 5,8cm F/1,5 at @1,5 @2 @2,8 @5,6



Sonnar 5cm F/1,5 at @1,5 @2 @2,8 @5,6



Sonnar 5,8cm F/2 at @2 @2,8 @5,6


