Vivitar 24mm f2.8 TX
Tokin made the Vivitar TX 24mm which I tested. My copy had marks on the rear element which probably affected performance. I tested the lens on my T2i with a Nikon F adapter. I found it difficult to focus on a slr. It would be much easier to focus on a mirroless body with a good viewfinder. The lens is made well and focus dampeming is very good. Aperture selection is a bit fiddly as the ring is slightly too small on these TX lenses.
Performance is a mixed bag. Sharpness is acceptable at f2.8 and tightens up at f4. Contrast is low. Colors area bit flat and there is some clipping in highlights. Fringing is viewable in extreme lighting. Bokeh is naturally smooth. Flare is an issue. Backlit scenes show a marked loss of contrast. Barrel distortion is also noticeable at all apertures. On a full frame body it may be too much to reasonably correct.
Okay, I made it sound bad. It's not great but it's not bad. I'm sure the marks on the rear element affected performance.