Originally posted by Aristophanes Tokina makes an 11-16/2.8 but not in the Pentax mount. However, that lens too needed to be stopped down to 5.6 at least at the 11mm to get decent sharpness.
Tokina AF 11-16mm f/2.8 AT-X Pro DX (Canon) - Review / Lens Test Report - Analysis
The Tokina 11-16mm at 11mm and f2.8; excellent in the center and very good at the edges
Compare to the DA 12-24mm at 12mm and f4; excellent in the center and very good at the edges
Compare to the Sigma 12-24mm at 12mm and f4.5; excellent in the center and very good at the edges
Compare to Sigma 10-20mm f3.5mm at 10mm and f3.5; excellent in the center, very good at the edge, and poor at the extreme edge
Compare to the Sigma 10-20 f4-5.6 at 10mm and f4; excellent in the center, very good at the edge, and fair at the extreme edge.
The new Sigma 8-16mm f4.5-5.6 at 8mm and f4.5; excellent in the center , very good at the edges.
Compare to the DA 14mm at f2.8; very good at the center, and good at the edges.
Compare to the Tamron 14mm at f2.8; very good at the center, fair at the edge, poor and the extreme edge.
Thank you
Russell