Originally posted by falconeye Bert, the shots were cropped from 300mm which is my longest lens to date.
Slightly offtopic, but I am looking into my options indeed and the Sigma 500/4.5 EX seems to one of the few options whch may still be usable free hand and has cropping potential. However, so far I couldn't find out how the AF works with the Sigma 1.4x TC and how much of a cropping potential the Sigma 500/4.5 EX really has. Esp. with 16MP APSC and 1.4x which resolve 150 lp/mm.
Falk, I have both the Sigma (the older 500mm f/4.5 APO EX) and the Sigma 1.4x. What do you need/want to know? I just sold my K-7 in favor of the K-5 (which I have not received yet), so I cannot do any serious testing for the moment (my *ist DS just does not cut it with regards to AF speed).
I agree on the handholdability, but only for short moments. I have been lugging the lens around handheld in the summer, but after 2 hours I was definitely quite tired. I then used a monopod but it didn't help at all; it just made the lens harder to use. I'd say that the Sigma is great to shoot from fixed locations (from the car, resting on a beanbag, or a doghouse blind).