Glass is not rated for resolutions like 12K or 8K or whatever, but in line pairs per mm. Some manufacturers publish such information in great detail (e.g. Zeiss). Others just tell you resolution limit, which doesn't correlate very well with perceived resolution.
See Otto Schade's research, for example referenced in this excellent paper:
http://www.corporacionvideo.com/pdfdoc/ ... nar_02.pdfSo, if you want to get even close to the resolution of 12K, use the sharpest glass you can find and expose it at it's best f-stop. Normally around f 5.6, maybe around 4 for fast glass. This is for S-35, larger sensors may look sharper at f 8, since you are further from diffraction at the same sensel density.
OTOH, if you want beautiful shots, use glass with the characteristics that fit the emotion and simply don't care
Any lens that can be adapted to the UMP 12K without extra glass involved will do then. I liked the look of a vintage Pentax Takumar 55mm f 1.8 on the 12K and resolution wasn't too bad either. Great for portrait on S-35. If you want razor sharpness for cheap, get the Sigma 18-35mm. A bit bland for my taste.
I admit that this post is getting a bit off-topic. If you want at set for cine work, the lenses John is referencing are some of the best you can get for a very decent price.