Sigma 500mm F4.5 lens
I also own this lens in the Pentax mount. A very good lens indeed. I find it really sharp at 5.6 and f4.5 is also sharp. Fast focus and sharp contrasty pic's. Deliver a very good photo. Highly recommended.
I give it a 4 because not focus limiter in Pentax mount or HSM. RE. screw AF.
This photo galery is dedicated to the Sgmai 300mm F2.8 and the Sigma 500mm f4.5 lens only.