After sending in the GR Digital III because of problems described here: http://ricohforum.com/phpbb/viewtopic.php?f=56&t=3104&start=10
, everything seemed to be ok until something went awfully wrong again. I discovered that this time, the problem seems to be limited to Spot AF only, but with similar effects to those described in my linked post.
I tried to focus on a plate with some food on it, but everything was horribly out of focus. The focus plane was some centimeters in front of the plate (which was about 30 cm away from the lens of the camera. I tried to focus on other objects and noticed that the Spot AF just failed almost every time I pointed the camera on moderately bright objects. Dark objects and those in the shadows did not seem to be affected at all. The focusing plane seemed to have erraneously shifted several meters towards me from 5 meters to under 1 meter.
So the problem seems to be limited to normally lit scenes, but when I changed my position (I tried several things like closing in on a painting on the wall, changing my angle etc), sometimes the focusing errors seemed to have vanished only to reappear when I changed my position again.
Then I tried other focusing methods like Multi-AF, Subject tracking and Macro AF, all of which yielded far better results than Spot AF (best results were achieved with Macro AF).
I suspected that infrared reflectivity could have played a role in the focusing errors (since the sensor is also sensitive to IR), so I checked the whole scene with a b/w infrared camera. Indeed, some of the objects (most notably the food) the camera failed to focus on where bright white, indicating a hight IR reflectivity. But results were rather inconsistant. Some objects that the GRDIII focused on flawlessly were also reflecting IR light quite well, whereas some objects the camera could not achieve focus on were not that reflective at all. And such a dramatic shift of focusing plane towards me is not quite possible with IR, right?
So, does anyone have the same problem? This is actually the third lens assembly in my GRDIII. Slowly, it mutates into an interchangable lens camera which is rather frustrating because it seems to spend more time in the repair center than in my hands. :/
I will also try to reset the firmware or something like that. Maybe it helps. But in any case, I will report back.