The Enemy! And His Finest Atribute.

I’m something of a B&L enthusiast. The exact reason is manifold, but likely started with a proximity based loyalty and it being the brand of my first stand. Today something from a competitor. -K

The American Optical Corporation was once one of the leading optical firms in the United States, if not the world. Well, honestly they never got the sort of press enjoyed by Zeiss, B&L, or Lietz. If you haven’t heard of them no doubt you don’t collect microscopes, or you’re not in the US. Perhaps AO Spencer sounds more familiar? Spencer Buffalo? In any case one of their finest innovations was something they called the Micro-Glide Stage. A simple apparatus, well executed and versatile, it’s something a wonder that it never became more popular.

The concept is simple, incorporate a floating stage of large size and circular outline on an otherwise stationary stage. By virtue of a large central hole the upper stage may be moved around the optical axis without the tedious turning of milled heads required by mechanical stages, or the fine touch (which takes some time for the student to acquire) needed in manipulating slides directly. Having used such a stage one quickly becomes adept at orienting the desired portion of any specimen. Because the stage is moved, rather than the slide one has the added advantage of not worrying about an errant stage clip knocking a cover slip from a temporary mount while chasing an active organism about the field of view.

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Simplicity itself

As one can see in this illustration taken from a maintenance pamphlet published by American Optical, the stage is almost supernaturally simple. No doubt the company used the simplicity of the Micro-Glide Stage to its advantage. Such an apparatus is far less complex than the circular mechanical stages seen on research microscopes, and would have provided American Optical a bit of an edge in marketing their microscopes to schools (an important client for nearly all manufacturers).

The utility of a rotate-able stage is not something one often has to convince a microscopist of, and no attempt will be made here to do so. Only, it has always been practice for schools (from grammar to graduate) to utilize a rugged and uncomplicated sort of microscope; it has however, been a rare thing for them to offer students the chance to use a rotate-able stage. For that reason alone many who use microscopes, even for professional reasons, have never made use of microscope bearing a rotate-able stage and will not feel the acute discomfort of lacking one.

While the great biological and petrographic stands with their finely machined circular stages are beyond the reach of most enthusiasts, or at least past the financial tolerance of spouses and parents, one can usually find an American Optical stand featuring a Micro-Glide stage for sale surplus or second-hand in the range of fifty dollars. At the risk of sounding the salesmen, I’d recommend searching one out. Below see a simple students model One-Sixty I prefer for looking at algae, living diatoms, rotifera, and all the bustle and huff in a drop of water.

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Divisible Objectives and my Favorite Stand

Things have come and gone in microscopy through the years. Some have been happily put aside as inconvenient when new advances were made and others have been quietly forgotten. I for one lament the passing of divisible objectives. -K

For a great many years it was considered abnormal and a genuine extravagance for a microscopist, even a professional, to be in possession of more than one stand. Optical apparatus was expensive, prohibitively so. Before continuing permit me to digress and provide an bit of example; consider that in the 1930 bound catalog of Bausch & Lomb an achromatic objective of 2x magnification was priced at $5.00, the equivalent of $71.10 dollars today. One could also have a 10x for $8.00 ($113.76). The full complement of dry achromatic objectives with magnification spanning 2x to 60x, some eight objectives in all, would have cost the princely sum of $86.00, $1222.93 in todays dollars according to the consumer price index, and been beyond the means of even the well-funded.

It’s easy to understand that for most microscopists it proved sensible economically to purchase a middle of the range 10x objective and use it with a comparatively inexpensive low power ocular when less magnification was required switching to a more powerful ocular as nessacary. In part because of the expense some things were done that would not be considered sound by the standards of today. One of those things, which no doubt seems somewhat blasphemous to todays workers, is the divisible objective. They turn up not infrequently on stands dating to what I think of as the “Black & Brass” era with rarer examples in the “Fully Brass” period preceding and becoming most common in the “Fully Black” period after the first world war. I can only hope for forgiveness regarding my rude designations of time but this is all very general.

A divisible objective is one in which the front and back optical components may be separated to obtain lower magnification. Bausch & Lomb produced these prolifically in the 16mm size so that with the front component in place 10x magnification was provided, while the rear portion only provided approximately 4x. By purchasing a divisible objective one was effectively provided a 16mm and 32mm objective in one unit. Most of the manufacturers provided divisible objectives of one sort or an other but the divisible 10x was certainly the most common from any source.

In 1925 Bausch & Lomb was granted a patent for a new system of constructing parfocal objectives that no doubt grew out of observations made while manipulating divisible objectives. The patent may however, have been an effort to cut down on competitors production of divisible objectives more than anything else, as the usual method of employing rings of varying thickness around the threads seems a great deal more convenient.

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For comparison

Above one may see a B&L 32mm objective, 40mm objective, and 32mm equivalent portion of a divisible 16mm objective. It’s worth noting the differing position of the optical components of the objectives and that any of these objectives will work usefully on a compound microscope. The stand seen below is a perfect example of the sort of microscope on which one could expect to find a divisible objective.

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No clips because I never incline my microscopes, it being my habit to work standing

The above is a Bausch & Lomb stand from the late 1940’s (easily dated by the double knurled heads). One can see the assembled 10x divisible objective in position and compare its outline with that of a non-divisible objective. This is in fact my favorite stand for micrography, photomicrography, measuring, and most general work, it shows every evidence of having been an economically prudent apparatus while not neglecting function.

This particular stand was assembled by Lukas Microscope Service of Skokie, Illinois. The company was founded in 1931 and is still in business today. They provided this microscope with a fixed, removable, 1.20 Numerical Aperture Abbe condenser with iris diaphragm and filter holder, the usual two sided mirror, and three objective turret. I keep a divisible 10x B&L, a 43x B&L, and a high dry 60x B&L in place on this stand and find few objectives more suitable for measuring the thickness of a mounted specimen than the 60x.

One final point concerning this lovely instrument, it is the most modern model I own which retains a draw tube. For any who are products of the modern age and have not had the pleasure I will say a draw tube can be unspeakably useful. Properly dispositioned it’s the work of a moment to compensate for an unexpectedly thick (or thin) cover glass, or increase or decrease magnification. Of course there are attendant sacrifices optically but I can’t count the times I’ve been able to better measure the size of a structure because I’m familiar with the workings of a draw tube for given combinations of objective and ocular.