Pentax-D FA 100mm F2.8 WR Macro Review
This lens has fast and accurate auto focus when used as a short telephoto and there is no hunting within the normal focusing range. This lens is thus perfectly usable as a walk-around, short telephoto lens for general photography. When using the lens for macro we recommend manual focus. This is not becasue the lens doesn't autofocus well (it does, and fairly quickly), but due to the radius of the auto focus sensors in the camera you will not necessarily get the lens to autofocus on the exact detail you want.
We used a K-5 for this test and have no reservations recommending this lens for K-5 users.
The lens relies on the motor in the camera for auto focus through the drive shaft mechanism; it has no built-in autofocus motor so the focus operation a bit noisy although not disturbingly so. The lens extends when focusing since it is not of internal focus [IF] design. We found auto-focus to be slightly slower than the SMC Pentax-FA* 200mm F4 Macro which is an IF lens.