Interesting Bellows - Ultra-Fine Adjustment

Anyone own one of these bellows:

http://www.ebay.com/itm/17090497824....m1438.l2649

This type has a very interesting feature. The diamond-shaped rail has a fixed inner rail and movable outer rail. The front lens mount screws down to the movable outer rail, but there is no "coarse" adjustment of bellows length like on many other bellows. Instead the lens mount is moved manually to the approximate position after unmessing with the locking screw. This allows you to move the lens in and out quickly to set the magnification. This is a similar concept to the Spiratone "rapid rail" which allows you to bypass the screw adjustment and slide the lens mount quickly along the rails.

So far this sounds like a low-end bellows with only coarse adjustment capability. But the bellows has a hidden feature: the round "trim" ring on the front is actually an ultrafine extension adjustment knob that adjusts the position of the outer rail vs the inner rail. Each turn of the knob equals 1mm of adjustment, so it's fairly easy to make adjustments in increments of a few microns! Each degree of rotation is about 3 microns.

I need to try this feature out for focus stacking and for setting precise magnifications.

Ray