Wednesday, December 14, 2016

Fastening the iris screws

This is the item in the cleaned-up wooden case.

This is another Bausch & Lomb microscope. A biological microscope with a 3-position revolving nosepiece, condenser and simple stage with clips. Came with the original 5x and 10x eyepieces and a 43x and 10x (divisible) objectives. Overall in great shape, the finish is immaculate and all the glass still very clean. This instrument was used with care and the case did its job of protecting it very well.

From the serial number, this fine instrument was made by the optical craftsmen at Bausch & Lomb in 1939 in Rochester, NY.

One of the two small issues with the instrument was that the screws that hold the iris assembly together were loose - this is not an assembly you want to have to piece together again...

Three screws (arrow) around the circumference of the iris hold it together. These screws are however completely inaccessible in the assembled instrument. To get at the screws, the substage assembly with condenser, iris and filter-holder needs to be taken apart.

The mirror pulls out, it is held by split-end of its pin in a hole. The substage assembly then can be driven down off its rack and pinion. Then the iris assembly screws off the Abbe condenser. Because the iris lever fouls the substage frame, the condenser needs to be unscrewed from the frame first. For this, remove the three screws around the condenser flange (thus also loosing the alignment of the assembly with the tube).

The iris assembly again tightened, the whole is screwed together again and fitted back into the frame. With care, the dovetail slides back on and the pinion onto its rack. With the three screws in the condenser flange not quite tightened, the assembly can be centered again.

Compared to e.g. typewriters, there is surprisingly little information online on the repair and adjustment of these instruments. However for the centering of the condenser, there is a very helpful paragraph in the small booklet 'Use and Care of the Microscope' by Bausch.

With some tweaking, the substage is again nicely entered in the view.

The other small niggle is that the fine adjustment does not quite line up anymore. It all works fine, but even at the top of its range, the two lines do not line up. Maybe it had a knock at some time that pushed down the fine-adjustment pawl, or it got serviced and not lined up then. (The line on the arm is very faint, just above the line on the moving part of the coarse adjustment.)

Perhaps indeed from a servicing - the optics and adjustments are all fine. These parts are a bit too tricky for now to tamper with. Leaving it as it now is - a perfectly serviceable microscope!

One of the slides that was in a small box in the case; small intestine. This particular microscope will be great for the children to explore the world of the minute :)

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