I was getting results like that with my enlarger lenses, but it was the film slightly sagging in the holder. Try using a glass carrier and compare. My EL-Nikkor 50mm f/4 is incredibly sharp on the entire frame @f/8. My Comparon 75mm (I know, not a componon... but it's optimized for the 8x10-11x14 range, and I couldn't tell a difference between it more expensive lenses at an 8x10) is also ideal at about f/8, except with Foma film, which needs f/16 because it's so curly and won't stay flat like FP4 and Acros do.