Sun Optical 24-40mm f3.5
I've just begun to test this lens. It is well regarded as the first decent 24-40mm ever made.
My copy has a PK mount which fits snug on my PK to Eos-M adapter. It is the re-branded Quantaray version. It handles reasonably well on my M3 but is difficult to zoom because of its weight. This lens is heavy and solid. Focus is very smooth though with less resistance than the zoom ring. Focus is difficult to nail though. Focus throw is reasonable and critical focus is achievable but the M3's screen isn't up to the task.
At f3.5 it's a little soft. At f4 and up it is sharp from corner to corner and I mean sharp. It is consistently sharp at all focal lengths and in macro mode.
To engage macro mode you must hold the macro lever up while you turn the zoom ring from 40mm to 24mm. I suggest using a focus rail with this lens. The focus ring is only good for minor adjustments.
I noticed some purple fringing in high contrast scenes from f3.5 thru f5.6. That may be this lens' only weak point.
Contrast is excellent at all settings. Shadow detail is excellent.
Color rendition is slightly cool. Saturation is moderate.
Bokeh is smooth and consistent.
This lens handles b/w very well. It produces images that feel like a Konica S2's image (see pic). This is high praise. The Konica S2 is special.
I look forward to testing in better light but so far I am impressed by this vintage lens.