Originally posted by Rondec The DA *55 is useless when it comes to tracking anything, even on a K3. Maybe very slow moving things. On a K-01 or using live view focus, it is really bad and racks the focus from end to end before finally settling on the appropriate focus point. I really like the lens for situations where I have time, but my wife gave up using it for wedding photography and now uses the FA 77 instead and is quite pleased with that (I think she is going to use the DFA 24-70 a lot as well).
I find the DA40mm F2.8 to (strangely enough) be quite fast and have to turn to that if it's a critical low light situation. Funny, you would think an F1.4 lens would be able to track better but not my lens. Like I said, this lens is great for a majority of things and if the lighting is good then it's usually pretty OK. Tracking though is semi-reasonable in bright light but go indoors and suddenly it starts to show some weaknesses. I know it's not a sport lens but I definitely need that extra bit of speed when things happen quickly.
The K3 would definitely be in my arsenal if I didn't already invest in another brand. However, not sure if the K3 will increase the speed of an SDM lens (Although it will probably focus quicker)?