Originally posted by WMBP
Have you ever used the Sony A550? I have been trying one out this week. The A550 can't compare even to a K20D, let alone a K7 or K5, in a number of ways: no weather-sealing, just one control dial, no video, and more. But it takes terrific pictures and the live view is surprisingly useful, QUITE capable of being used for normal shooting (if you don't mind the drain on the battery). Reviewers noted that the A550 was the best in its class at the time of its release (little less than a year ago), but gosh, it's good. And I expect the forthcoming A55 DSLT will be even better. That's what I'm comparing against the Pentax here.
Will
For every DSLR with mirrors, you're still better off using the optical AF system. AF in LV will always be slower because it's just a software algorithm like in P&Ss. And yes, it drains your battery, another reason why it's meant for studio/tripod work, not for shooting out there in the street.
In my opinion, there's no point on buying a DSLR to use LV all day. That's just silly, you're exchanging improved AF and optical viewfinder for crappy AF and a low-fidelity backlit LCD. You don't get better resolution and color fidelity than real life, you know?
Now: does this Sony model features a *mirror* or *prism*? If it's prism, it's using phase detection AF even in LV, which is another system altogether. While it allows to use AF in LV, there's a trade-off which is making the optics darker and less light hitting the sensor.