Originally posted by philbaum In static low light focusing, i believe the K3 is better than most cameras out there. When i've tried AF tracking, it works fine when tracking flying birds at a distance, but up close, the K3 fails and other cameras would fail at some point as well. I don't believe there's been any hard repeatable testing of the K3 or any camera's tracking ability - its mostly annecdotal or limited comparisons for a certain situation.
If a lens is going to quickly follow the focusing commands from the camera body, the internal lens adjusting mechanism has to be lightweight and the lens motor must be very strong. With the new FF lenses and the new FF body, Pentax has a chance to improve the AF tracking of its flagshift camera.
For static low light focusing, the K3 will beat its Nikon and Canon APS counterparts hands down. I can't believe the K3 is as cheap as it is today - between $600 to 700 i believe. What a bargain.
You touched on, but didn't really hit on a point I also wanted to try and make...
And that is...I think the speed of the lens effects the camera's ability to do continuous AF tracking well, because even though it is the camera CPU & software doing the tracking by reading off the sensor or Fresnel, it only has what it gets through
the lens glass as "data" to work with.
So for example, if the little crumb cruncher is running at you fast, and you have perfect focus on the first step, but the lens motor doesn't re-focus fast enough on the second step towards you, then the computer now has a less sharp, lower contrast image in its field of view and if it doesn't reacquire a high contrast sharp image in the next focus step, then by the third step towards you it will be so soft that the acquisition will be lost and it will be too late and have no chance of catching up then it starts hunting. At least this is what I see in practice.
To drive my point home, what I guess I'm trying to say is that perhaps newer faster lenses will make the existing CAF work better, and the problem might not be with the CAF software or hardware in the camera. The speed of the screw drive in the camera of course could effect CAF as well, but I've always thought screw drive had already pretty much reached it's limit of performance and there is nothing more to be really gained there and that any real improvement in AF speed will have to come from in-lens motor electrickery.
Eric