Hi, has anybody ever had the opportunity to compare FA-20/2.8 and DA-21/3.2 side by side? Are they better than DA 18-55 on the short end, WRT distortion, vignetting, and so on? Why should I consider a full frame 20, owning a K-18/3.5? Or maybe DA-21 outperforms the older 20s? TIA for all answers! Pancho