Originally posted by Digitalis There aren't any FX format f/1.2 lenses with full AF in the Nikon system. Only Canon have AF lenses from f/1.0 - f/1.2 - and trust me you wouldn't want to use tracking AF with an f/1.0 lens on any canon DSLR - my 1Ds MKIIN could probably do it, though with a 90% failure rate.
Thanks for the reply, but what I stated was F/1.2-2.0 with Nikon AND Canon. More precisely the Canon 50 1.2L and Nikon 85 1.4G. I didn't mention f/1.0 at all but that has more to do with the lens build and the poor AF on that lens more than anything. Tracking AF with the 50 1.2L was about 50% dead on, sometimes better. My question is not the physics of the thin depth of field or predictive focusing (which somehow everyone always ends up talking about), but the fact that with the right technique and the right gear, 1.2/1.4 can be used to track moving subjects with some accuracy, and I prefer that. Even for portraits, I like my subjects moving. I've been shooting weddings for about 7 years so I understand that it's much easier to stop down to gain accuracy when your system just can't hang, but with Nikon I never had to. But that is what separates good systems from great ones. With Nikon, it was deadly accurate at 1.4. With Canon, relatively accurate at 1.2, but not any better stopped down to f/1.4 or f/2, so it wasn't the depth of field. But I'm at a point where I have a very specific image quality/rendering in mind and don't want to do a whole lot of post processing, and Sony and Pentax have what I need to get what I want in-camera with little to no processing.
To clarify, my question is...how is Pentax AF in comparison to the big 3? I don't really need to know about focusing physics in general, just a point of comparison. Thanks. Are there any other wedding photographers using Pentax? Here's an example of subjects moving towards me relatively rapidly, shot with a 50mm at 1.4 with a Canon 5d3.