Its the bodys assigned job to determine when those light beams are in focus. Theres nothing within the lens to calibrate. The only focusing info that comes from an SLR lens is the light beams coming thru the glass. IOW, you are calibrating the bodys own internal focusing device, but nothing in the lens. There is artifice involved and thus a possible difference between the analog and the reality.Īny AF calibration performed will be to deal with the difference between the non-sensor focusing device (Leica RF or SLR AF module) and the actual sensor image. OTOH, if its gathered from some other source such as a Leica rangefinder or an AF SLRs AF module, those other sources are only analogous to the real image focused on the sensor. If your in-out focus data is gathered from the image sensor then theres no reason for focus errors. For me, I prefer to assume nothing and to conduct carefully controlled experiments. One can certainly question whether the improvement is noticeable or have lenses, new or used, that are optimal. Nonetheless, I have found that my lenses improved by recalibration, also known as microadjustment. If my explanation is wrong, then I will admit to that. As you said, that challenges common sense.
