Upload & Sell: Off
1) Is the 1.6 m. minimum focusing distance a problem? It has not been for me (my usage: landscapes, large nature details)
2) What is the best performing aperture? / f/4-f/11, f/2.8 is slightly soft but at f/4 it's OK, f/11 is usable and due to good micro contrast prints still appear very good. As you can see MTF for f/2.8 is pretty OK and f/5.6 performance is very good, I have not seen f/4 MTF but based on actual photos taken by lens and evaluating on screen & large prints I would estimate f/4 won't differ that much from f/5.6 (pictures from Zeiss PDF):
3) How does the lens perform fully open? It's slightly softer (see MTF above) but contrast is very good already wide open as well as micro contrast, for a 100EUR I was positively surpriced
4) Has the lens any colour issues - e.g. with yellow colour?no
5) Has the lens any balance problems when mounted on the camera - e.g. nose heavy?I used with 5DmkII: no, it's very small and light lens
6) Any other issues worth mentioning? Bokeh CA is horrible, against bright background dark objects (like branches against white show) get green borders back of subject and magenta in front of, example f/5.6:
What I specially like in C/Y 135 is the transition from DOF to bokeh, to me it looks very natural and I can separate subjects from their surroundings at f/4-f/8 just the way I like. I also like to use the natural transtion to bokeh my doing 5x4/4x3 image panoramas to use the same effect on wider view.
I did buy recently M42 Carl Zeiss Jena Sonnar 3.5/135 and have not yet done comparison between these two but it appears that f/3.5 has even better bokeh, but haven't studied the transition from DOF to bokeh yet. f/3.5 version focuses also closer (1m), and my initial test photos indoors appear to be very good.