I was never particularly fond of it being called an elementary or a freshmen microscope, but call it as you will. -K
A student microscope is generally simple, rugged, and basic. Where a more advanced stand will have stops and set screws, adjustments upon adjustments, and provision for all manner of accessories, a student microscope will be without. The photograph today shows a representative microscope of the type by Bausch & Lomb which dates to approximately 1930, this particular example saw service at the University of Kentucky school of zoology.
It has the usual things, coarse and fine focus, rotating nose piece with RMS threads, stage with stage clips, inclination joint, rotating circular substage diaphragm, and mirror reflector. At first glance except for the absence of a substage condenser one might be forgiven for taking it as fully as complex as any microscope of the period. However, a brief look shows that this is not the case. The substage mirror is only single sided, and that single side is the a secondary concave reflector∗. A moment of manipulation will show that the mirror is mounted an arm and post with no positioning stop to provide confirmation of when the arm or mirror are aligned vertically.
There is no provision for the use of filters between the light source and the object. No mechanical stage is present and as a result of construction one can not be conveniently attached. The stage itself, and the microscopes foot are sure to seem small to those accustomed to more contemporary stands, and it is on the smaller side† as microscopes go when compared to more advanced stands from the same period.
Unlike even moderately more advanced stands, the fine adjustment has no provision for measurement. Where a more costly stand will show markings on its fine focus so that a specimens or structures thickness may be measured in divisions of a few microns or less, on the student stand there is only bare metal. One might think this is done to save time in manufacture, a graduated knob surely taking longer and costing more to produce, but it is more complex (or rather less). The fine focus on a more advanced microscope is graduated as a feature, because it can be. It is constructed in such a way that from its lowest to highest limit a a turn of the knob of a given distance will result in a consistent amount‡ of upwards or downwards focus. A student microscope will often show a variation in its vertical travel as one moves through the range covered by its fine focus.
Without a substage condenser there is no reason for a complex external illuminator. Most students misuse both condenser and illuminator even under the watchful gaze of their teacher so doing away with both is as much a matter of efficacy as it is of economy. The rotating diaphragm is mechanically very simple and prevents as much as it may the abuse of the diaphragm to control light intensity as well. Without a condenser the concave mirror alone will serve effectively for the provided objectives.
Only two objectives are apt to be present on a student stand. The powerful 43x will operate at the limits of its ability with the mirror and a properly positioned light source. The 10x is likely to be one of the divisible sort that may have its front lens removed so the base may serve as a 32mm objective. Once chief characteristic of proper student microscopes (worlds apart from toy microscopes) is standardization. The objectives on this economical Bausch & Lomb unit are identical to the standard compliment of achromats provided on much more expensive models. The oculars as well are identical to the usual Huygenian sort although, only the 10x is apt to come standard. An educator might have easily purchased a number of 5x, 12.5x, a set of wide field oculars, or a few filar micrometers to share out among a class as required. Todays user might easily find replacements for damaged optics or a variety of oculars to suit their needs.
One might expect that an elementary microscope will only provide passable images. As the objectives and oculars are identical to those of much more advanced microscopes, and complex substages are often operated such as to be useless, there is no reason to achieve less than excellent results with a simple, economical§, students microscope. Given the choice of a students microscope from the 1930’s and a students microscope from today one will find the vintage microscope fully as capable and more deserving of ones time.
A contemporary students microscope is apt to be targeted in its selling points not towards the institution, but rather the inquisitive student themselves or more likely the students well intentioned parent. This has led to a focus on magnification as a selling point and a certain degree of complexity being mistaken for capacity. One will find microscopes offered for student use with three and even four objectives, two and three oculars included outright, complex substages and “focusable” LED illumination.
With fewer optics to choose from one is limited in their choices for magnification‖, and far more likely to make the correct choice. In have a less complex microscope one has perhaps less opportunity to get into bad habits and certainly less capacity to decrease the quality of the image formed by improper disposition of the instrument. At the simplest a students stand should be able to immediately form an intriguing image for the user. With this old soldier one need only turn on a desk lamp, position the mirror to direct a cone of light through the stage, place a slip under the clips, and (due time taken to perform the microscopist’s obeisance) turning the focus knobs bring something interesting into view¶.
In a moment a world can be revealed, shown with fully as much clarity as any microscope apt to find itself in a students hand. The work that has been accomplished on such microscopes would stagger in its scope and quality. A simple compound microscope suitable for common use in all but the most exacting applications, the classic students microscope is as useful today as it has ever been.
∗Secondary reflectors are much more common than primary reflectors. On a secondary reflector one reflecting surface is covered over by a second (generally far less) reflective surface. A polished metal mirror is a primary reflector, a reflective surface covered by glass is a secondary reflector. Secondary reflectors are inherently imperfect and may result in a ghostly secondary reflection in the image plane.
†The size of the stage and foot will not seem out of place to those familiar with microscopes from the turn of the century. The trend towards larger stages and very large footprints is considerably recent as far as microscope evolution goes.
‡It is not very uncommon to find a microscope of over well over one hundred years age the fine focus of which is as tight and responsive as the best microscopes of today. Many different fine focus mechanisms exist and the best of them are simple (comparatively speaking) and reliable in a way that compares favorably to those of today. They might not impress a watchmaker, but any machinist will find them beautifully constructed.
§In this post I switch at times when writing, between how the microscope might have been employed when new, and how it might be used today. When I describe it as economical it applies both to when it was new and even more so to its value now. The microscope pictured cost me less than twenty (US) dollars and is not some rare and seldom available specimen. In the right hands a microscope of this sort will provide results consistently superior to a modern entry level microscope that commands a price ten times higher.
‖Never mind the correct or most suitable magnification for owns aims, one is apt to spend far more time looking at things and far less time twirling the nosepiece about like a maniac. I see “student” microscopes offering 40-1000x 40-2000x and want to have these charlatans arrested! But then what was I saying about maniacs?
¶A modern student might be troubled first by the hunt for appropriate batteries or power cords, potentially difficult to obtain replacement bulbs and even electrical adapters. With the lighting secured but before placing a slide upon the stage, they must puzzle out the usage of the stage clips; as those on modern stands seem to have been designed by persons with no knowledge as to how they are employed! Then the proper objective and eyepiece must be determined or as is far more likely chosen at random. By this time if interest has not waned they must fiddle about and focus and image that is apt to prove far to highly magnified for their use (beginners have a not unexpected tendency to select powerful magnification initially) and will likely mangle a good many covers and slides in discovering how short the working distance of a high power objective is.