Questions on Zeiss Stereomicroscope III

[enricosavazzi]

I have a Zeiss Stereomicroscope III (the older all-metal scope with black zoom knobs being the only plastic parts, not the more modern plasticky Stemi).

The zoom knobs have click-stops at 1x, 1.2x, 1.6x, 2x, 2.5x, 3.2x and 4x magnifications. The click stops are a bit hard, but the zoom knobs rotate with little resistance once the "threshold" out of a click-stop has been passed. My questions are with respect to this click-stop mechanism.

• Is it possible to remove the click-stops and let the zoom knob rotate smoothly? Alternatively, is there a way to adjust the click-stops to require a lower force to rotate the zoom knob?

• Does removing the click-stops involve a risk that the zoom will slowly "sag" to the lowest/highest magnification instead of remaining at the set magnification? If so, is there a way to adjust the friction of the zoom knob after removing the click-stops?

• Does anyone have a service manual for this microscope?

[genera]

In regard to sagging you could try, as a first step before taking anything apart; setting the zoom to some intermediate position, 2.5x for example, making a target that exactly fills the field of view, and then coming back a day or so later and comparing the fov to the target. If there's been some sagging then you probably can't remove the detent. If there was no sagging then you could try the same experiment without the detent. Once you gotten to this point you should be able to tell whether or not there's an adjustment mechanism.

If there's sagging after the second step you could reduce the force the spring exerts. If it's a leaf spring by carefully bending it or possibly by shimming the stationary end. If it's a coil spring by replacing the spring with one of the same size that exerts less force or alternately by removing a coil or two.

You could also modify the profile of the detent grooves by filing away their sharp corners. I mention this last because it's the hardest to restore.