Originally posted by Scorpio71GR I would suggest a DA*55 1.4 although it is not cheap. I also have the Rokinon 85mm 1.4 which is essentially the same lens. That is pretty much a head and shoulders lens on crop sensor unless you get far enough back. I find my Rokinon 85 not the easiest lens to focus precisely. On a crop sensor the 55 1.4 would give the results I think you want. There is also the Sigma 50 1.4. I love my DA*55, on the K-1 it is magical.
I'd second Michael's opinion, the DA* 55mm f1.4 is the way to go, very sharp from f1.8 to 2.8, shallow DOF, superior contrast, colors (Zeiss Otus -like character IMO)...excellent in all regards.
I don't own the Rokinon 85mm unfortunately but I've handled many 50-85 lenses in the past. Here's a medley of pictures taken with different lenses same subject, Sigma EX DG 85 & 50 f1.4, Sigma EX DG 50mm, Da* 55mm f1.4, -F 50mm f1.4, Supertakumar 50mm f1.4 (8 elements) (made an flickr album
cat pictures | Flickr
(the King of the heap) Sigma EX 85mm @ f3.2 (Pentax K5)
Crop
Sigma EX DG 50mm f1.4 @ f2.0 (K3)
crop:
Pentax DA* 55mm @ f2.0 (K3)
crop:
Pentax -F 50mm f1.4 @ 3.2 (on K5)
and my favorite: Super-Tak 50/f1.4 8 elements @ f1.4 on K3
crop: