Terrance

China’s market, they recycle broken devices and sells parts.

Appended some steps about the sensor. In case you’re interested.

Tear it down and see what’s inside.

This is a professional lens, built very tough. Primary mirror cleaning is quite easy. but front element is kind of tricky. because there’s an inner thread there covered by damping oil/grease. Maybe you should try remove it from the front. remove the filter/cap thread ring first(My cap used to stuck with this ring so I‘ve got this far)…

In step 3, there are 2+3 screw holes at each end , those are for focus ring stopping screws. 3 for inf end and 2 for close end (if my memory is correct). But this is for adjustment instead of “calibration“. By my guess a giant lens like this could never be calibrated due to the TCE of aluminium tube. that’s why the focus ring is allow to go beyond inf.

Never get to know by just thinking.

hmm, haven’t dug that deep yet… The front case disassembly seems very tricky. Also the IR-cut removal.

Good as brand new :D. I used “super glue“ and learned the lesson. Luckily the mess is not very bad, cleaned that up and the great lens is happy again.

It does. And might be worse, because MF sometimes goes faster than AF, then stuck deeper…

isn’t a powerbank a better choice?

sure … XD