Ummm...why does Canon or Nikon even need lens calibration in their cameras? Are their engineers just sloppy with lens/camera tolerances? ![Shocked :o](https://forum.luminous-landscape.com/Smileys/default/shocked.gif)
Canon and Nikon both have lens calibration, AKA micro-focus focus adjustment. Both of them keep the adjustments in the camera, not the lens as Sigma does. Using Canon as an example, you calibrate the focus at one distance, which they specify as 50 times the focal length, though many use 25X instead. You calibrate their zoom lenses at only the telephoto end on older cameras. Newer cameras are calibrated at both the telephoto end and at the wide end. Sigma takes this a step further by calibrating zooms at the telephoto and wide end as Canon does, and also at intermediate focal lengths. And, instead of calibrating at only 50x the focal length, they are calibrated at 4 different focus distances, from near to far. It's better to keep calibrations in the camera since each camera may be different, but Sigma has no control over that so it's stored in the lens.
edit: I should also add that calibrating a lens at one specific distance does *not* necessarily mean any or all other distances will have the same focus accuracy as the calibrated distance. If they did, manufacturers wouldn't specify any particular calibration distance. Only the particular distance (and zoom setting for zooms) can be guaranteed accurate. The rest are within some tolerance of that, and reducing tolerance is what MFA is about. That's all a matter of linearity of the design. If these mechanisms were perfect, you wouldn't need MFA adjustments at both ends of the zoom range, for instance.