I also own the F 50 f1,7 (and love it). To me it delivers really neutral results, not really blueish. The A-50 (f1,4) I had before did give a warmer tone to pictures, and so does my Sigma 17-70, so you could say the F is cooler in comparison. However, it looks just like what my Pentax FA 100-300 delivers, so I would not call it a colour cast.
Quote: would believe that a blueish tint on the coating will give you a cooler color cast.
If you can
see a blue reflection, it means blue is reflected, not let through...