The reason for the movement is due to the central spindle bolt coming loose, or being worn by the contant focusing movement.
To erradicate this movement you will need to put in an extra shim washer between the two focus arms where they join on the central focusing spindle.
The shim washer should be in the order of 0.1mm. You remove the IPD scale which caps the spindle. There should be a large bolt with a straight slot on top that has to be removed. BEFORE you do, there are two things to be careful about.
1) is that there could be a set grub screw holding the bolt in place or 2) the bolt is held in by an extreme form of locktite. It's easy enough to loosen the grub screw, but the locktite is a real beast. You make have to remove the screw at the other end of the axle and, with a fine flat blade screwdriver, remove the spindle lock bolt from the other end of the spindle. Once you have done this you rotate the focus wheel to remove the eyepiece assembly. Clamp this above the multistart thread in your vice and rotate a COUPLE of degrees at a time anticlockwise then clockwise over and over until the bolt releases.
This is so you don't break off the locating pin on the left hand arm. You can then take off the focus arms and insert the shim washer using a touch of grease on both sides. Assembly is the reverse. Ensure that when the focus wheel reaches the end of its travel that the focus arms are all the way in. That means your binocs will reach infinity focus.
If you have trouble doing this job
, take it to an expert
Also belong to a couple of useful groups one being the Antique Telescope Society and the other a binocular group. I have always enjoyed restoring these types of things! Most are love jobs(
) that you can spend hundreds of hours on, but how do you charge someone $6,000 for a repair?
Ohh well, back to the grind .... sorry, polish now.
