The essence of the bug:
When the mode dial is rotated to or through the GREEN mode or the USER mode, the AF Fine Adjustment resets to zero and stays zero until you reboot the camera or press the menu button.
Details:
My testing showed that if the mode dial is being rotated from any mode other than GREEN, USER or Video into the Green mode or USER mode and then back, the AF Fine Adjustment value is being reset to zero and stays there (which can be confirmed from the EXIF or actual focus in the image). However in the Green mode itself (and the USER mode) the AF Fine Adjustment value is always the original one (the one you set). Note I did not do precise tests with focus charts to confirm for sure if the focus actually shifts. My unprecise tests seem to confirm that as well as the reports from the user who has pointed out the bug to me (I do not know how precise his testing was).
Going into Menu or turning the camera off and on returns the AF Fine Adjustment setting to the value you have set it to.
My equipment:
Pentax K-5 FW1.14 + Tamron 17-50 f2.8 AF Fine Adjustment set to -10. Pentax DA 40mm f2.8 Limited (tested both with +10 and -10)
History:
The bug was pointed out to me by
Kerusker on another forum. He thought the reset happened after shooting a short video or using the USER mode. However my testing seems to confirm that it is actually rotating the mode dial through or even to-and-back the Green mode or the USER mode is doing the reset.
Kerusker mentined that he noticed the behavior in 2011 with K-5 FW1.10 +DA 55-300mm. He has reported the bug to Pentax Germany and according to him Pentax Germany has acknowledged the error. Subsequent FW updates did affect the exact behavior, though never fixed it according to Kerusker.
The impact of the bug:
The bug may be quite serious if you rotate the mode dial through the GREEN or USER modes when you operate the camera. Especially if your AF Fine Adjustment values are extreme. The bug completely defeats the purpose of AF Fine Adjustment feature in this case.
Work-around:
Pressing the Menu button after returning the mode dial from USER or GREEN mode. Turning the camera off and then on.
Update: the issue is still there with firmware v.1.15 on K-5
Last edited by vanyagor; 09-15-2013 at 02:17 AM.
Reason: updated for newest firmware v1.15