Chiming in now - hope issue was solved in the meanwhile.
To properly set the autofocus to work, you need to raise/lower the entire column by unlocking the column base with the focus variator handle on the right and raising it/lowering it with the handle on the left, and then lock the column again. In theory, the height indicator should correspond to the height of your easel - or zero if you don't have any easel. In practice, put a test negative in the carrier, and use a standard focus finder to set the column height.
Once this is set, L900 keeps the focus when you raise/lower the head, for about 2/3 of its excursion, mainly in the central zone. It may lose focus at the max or min height. In that case you need to adjust the focus with the knurled ring around the lens.
The two knobs on the right of the head are: the outer (larger) one is to lock/unlock the head, the inner (thinner) one is to do micro movements when the outer knob is locked. In practice, you unlock the column with the outer knob, set the head at a given height, lock the head with the outer knob, and then use the inner knob to precisely set the column height for a certain enlargement. Those two knobs are NOT used for focusing, but only to set the enlargement.
Looking at your video it seems that the outer knob does not lock the column, therefore the inner knob can't be engaged. It should not be a major problem to fix. I own the repair manual so if you still haven't solved send me a PM and I will try to help you.
Last edited by LikeAPolaroid; 12-28-2012 at 06:57 AM. Click to view previous post history.