There seems to be confusion about whether PhotoScan is capable of solving a complete and accurate lens calibration. And yes, it is very capable of doing so if proper photos are taken.
The best field practice is to use auto-focus once, make sure the photo is in focus, and then turn off focus entirely. Even better, tape the lens so no accidental change is possible. Sadly, taping some lenses will not actually accomplish anything but it might serve as a reminder. Capture a set of images from the same approximate distance to insure that all photos are in proper focus. By a set, I mean take proper overlapping stereo photos in landscape mode and then take a few additional photos of the same subject area as the landscape photos, with the camera rotated to portrait. It is better to rotate both clockwise and counter-clockwise for additional portrait photos. With all photos captured in a set with no change in focus (or zoom if using a zoom lens), make sure all photos in a set are grouped in a camera calibration group.
You can take another set of photos from a different distance and you should in fact refocus to make sure your images are not blurry. You should take a complete set - with some rotated - and make sure the new set is grouped in a separate camera calibration group. Both sets will be calibrated at the same time if separated into groups - in the camera calibration dialog box.
A high quality lens calibration is not a trivial thing but can be made to seem so if proper images are taken and optimized thoroughly.
Tom