Some Early Microscopes from the Optical Institute in Wetzlar

(authored by:  www.antique-microscopes.com)

Certainly, most microscope collectors are familiar with the firm E. Leitz, Inc. and many of them probably have several Leitz microscopes represented in their collection. Some, however, may not realize that the founder of the firm was not Ernst Leitz I, but Carl Kellner. Kellner founded what was named the Optical Institute in Wetzlar Germany in 1849. By 1851 he employed twelve workmen and was producing his first microscopes. Among the more notable graduates of the Institute was one, Ernst Gundlach, familiar as the designer of the first Bausch & Lomb stands, who was employed during the years 1859-1862. ¹ Other opticians who at one time worked at the Optical Institute and later founded their own firms include Riechert and Hensoldt. ² Kellner's microscopes met with wide acclaim and were furnished with his noted invention, the orthoscopic eyepiece. While first applied as an eyepiece for telescopes and then later adapted to the microscope, it enables a large flat field of view.

Unfortunately, at only the age of twenty nine, Kellner succumbed to tuberculosis in 1855. The Optical Institute survived under the leadership of Friedrich Belthle, an apprentice of Kellner's, who married Kellner's widow shortly after his death. In 1863 Ernst Leitz joined the Institute. By 1865 he was a partner in the firm, and later became the sole proprietor after Belthle's death in 1869. For some biographical information about Carl Kellner, link here . In the pamphlet Leitz Microscopes for 125 Years ³ , it is mentioned that during this early period of the Optical Institute under Kellner's and Belthle's leaderships, three different models of microscopes were manufactured. For some years, I have had one of these microscopes represented in my collection. More recently, I was fortunate in obtaining another different model. I was able to locate an example of the third model in the possession of a fellow collector. Since, as far as I can tell, descriptions of these early Wetzlar microscopes can not be found in the usual sources, I thought that others interested in the history of the microscope might be interested in learning about them.   

Assigning dates to the microscopes that will be discussed herein was made possible using information contained in the aforementioned Leitz pamphlet that has a table giving the average number of microscopes manufactured during ten year intervals starting in 1851. These data were plotted for the years 1851-1870. The best linear relationship was found and then integrated giving a binomial expression that correlates the serial numbers with the dates of manufacture. It should be noted that the serial numbers found on the later Leitz microscopes derive from the same series as these earlier Kellner and Belthle stands.

The earliest of the three microscopes is shown in Figure 1. It is also the most elaborate both in terms of the accessories associated with it and its mechanical movements and it probably represents the top of the line in the series. The microscope is signed on one side of the limb " C. Kellner in Wetzlar" and on the other " Belthle and Rexroth, No. 451" . It was made in 1861. Following the death of Kellner in 1855 and beginning in 1857 there was, for a brief time, a partnership between Belthle and H. Rexroth. ^{2 ,4} Whatever happened to Rexroth and whether he continued in the microscope business after the partnership dissolved remains unknown to me.

by push tube. The outer tube is sprung and contains an adjustment screw that allows the tension to be altered. The fine adjustment mechanism is identically constructed as in the previous example. The round stage has an oxidized brass finish. There is no provision for stage clips. Inset under the stage is a wheel with five apertures. The microscope has no provision for an additional substage apparatus. The microscope was found cased with three eyepieces numbered I, III, and V and four objectives the number 1 is signed " B.L." , the numbers 3 and 7 are signed " Belthle & Leitz" , and the number 4 is unsigned. Also found with the microscope is a hand written magnification chart listing the  various magnifications obtained using the different combinations of eyepieces and objectives. As stated above, this microscope could be dated to 1865 from its serial number. It was also in this year that Ernst Leitz became a partner in the firm. From the signatures on the microscope and the objectives, it would seem that the microscope was made immediately before Leitz became a partner while the objectives were made after this event. It is therefore likely that this microscope, with its associated objectives, is one of the first articles of commerce bearing the Leitz name.  This microscope is very similar to Kellner's original model.

The last example is shown in Figure 3 and it is the simplest of the three models. The microscope is signed on one side of the limb " C. Kellner's nachfolger" and on the other " FR. Belthle in Wetzlar, No. 895" . It can be dated to 1864. It is 11.5 inches tall as shown in the figure. The square iron base is painted black and has an attached short iron pillar that supports the main body of the microscope. This model does not have any provisions for rotation about the optical axis. The single sided concave mirror is attached to a short arm mounted below the stage. The coarse and fine adjustments are constructed in an identical manner as in the previous example. The square stage has an oxidized brass finish there are no provisions for stage clips. Inset under the stage is a wheel with 6 apertures. The microscope has no provision for an additional substage apparatus. This microscope was also found with its case and a number of objectives and eyepieces. The objectives represented are numbers 1 and 3 signed " FR. Belthle" , and a number 0 signed " FR B" . The three eyepieces are numbered I, II, and III. 

Overall, these microscopes were extremely well constructed. The mechanical movements are still smooth and without lost motion. Most commendable in each of these models was the incorporation of various adjustments to the focusing mechanisms that could compensate for wear. Such adjustments were usually absent in contemporary microscopes and in many that came later.   

figure 3

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