I know a lot of people say this lens is very sharp, but that isn't my experience. This lens is not able to resolve fine detail at all. I am wondering if this is a normal occurrence or if I may have a lens with abnormally poor performance?

If this is normal, would the 50 1.4 improve sharpness and fine detail?

Here are two sample images. The one of the full mouth was taken using the 50mm f/1.7 at f/8. The one of the side of the mouth was taken with the 100mm f/2.8 (not the Macro, the M-series prime) at f/8. Both shot at 1/75; the sync speed of the LX using soft box camera right.

These were both taken at the same time using the same lighting on the same Pentax LX camera using the same roll of Portra 160 film. The film was scanned using a Plustek 7400 scanner at 7200 dpi, down sampled to 3300 dpi and cropped to the sample shown. The only prints I have are at 4x6, and they both are acceptably sharp at that level of enlargement. It's only blown up, as I would do if printing 11x14, that the 50mm becomes unacceptably soft to me.

At first I chalked it up to a focusing error on my part, but every 50mm shot on this roll is soft, and every 100mm shot is sharper with more fine detail.

Any input? Thanks!