SP> I tried both on Nikon D70. Tokina has worse sharpness than Sigma at open
SP> apertures and has much higher chromatic aberrations (probably because Tokina
SP> uses just 1 ED element while Sigma 4). And Sigma has much faster AF thanks
SP> to true IF, is lighter despite having very good build quality (not as tough
I too found out a lot of purple fringes - I attributed it to flare
though. God knows what it was. But remember that the Sigma in Nikon
mount uses HSM - their equivalent of ultrasonic motors. These do make
the focusing a lot faster, especially on a body with weak AF motor
like the D70. I think on Pentax the difference wouldn't
be big?
Good light!
fra
