SMC Pentax-DA* 60-250mm F4 ED [IF] SDM Reviews - DA Zoom Lenses - Pentax Lens Reviews & Lens Database
After running into problems while using my Pentax DA* 60-250mm lens to shoot a basketball game today, I must say that I'm really disappointed by the way the AF mechanism is designed.
It seems the main source of the issues with this lens' AF is the hybrid screwdrive/SDM system. The Quick-Shift Focus System is supposed to prevent the user from turning the focus ring while AF is in progress; however, it seems that when combined with an in-lens SDM, this mechanism can lock up or cause excessive friction, resulting in sluggish AF performance. In some cases, the lock may fail to disengage properly and lock up the focusing mechanism altogether until the lens is dismounted (suggesting that the screwdrive AF coupler connection is part of the issue).
Be sure to read the updated review for more on this issue. At this point, I really cannot recommend this lens for serious professional use as it's just too unreliable. I've gone through five different units and I just don't feel I can trust it to work properly.
I am replacing it with a D FA* 70-200mm in a few days.
Draco