Among the accessories are four eyepieces, two double-sided side mirrors, the vertical illuminator, a cased centering slide, and two apochromatic objectives in special short mounts labeled 4 and 16 mm for use with a vertical illuminator.
There are other empty slots in the door, one of which likely held a larger side mirror.
The following description and illustration was taken from Catalog B, Microscopes
and other Apparatus for Biological Laboratories, 1923, Eimer & Amend, NY.
ZEISS MICROSCOPE ISB. Recommended for use with vertical illuminator.
This model has the large Zeiss mechanical stage, but stage can be raised
and lowered in the direction of the axis of the microscope by means of
rack and pinion strongly constructed so as to carry heavy specimens.
This arrangement is very important, as it enables the coarse adjustment
to be made without disturbing the position of the body tube. Thus
when an object is studied by incident light (in the case of high
powers with the vertical illuminator) the relative position of
the body tube to the source of light need not be disturbed;
the fine adjusting is done in the usual manner, the slight necessary
movement not interfering. If for use with vertical illuminator, short
mounted objectives should be used.
As shown in the illustration, this model can be outfitted
with a full sub-stage for use with transmitted light. However, the example shown on this page was supplied
without a sub-stage, but with a vertical illuminator. Evidently, it was only used as a dedicated metallurgical instrument.
The following description of the Zeiss Vertical Illuminator was extracted from the 1913 catalog:
Illumination by Incident Light.
For the examination of opaque objects, metallurgical specimens, etc. it is desirable and often necessary to provide a suitable device for adequately illuminating the object from above. When the free working distance of the objective is sufficiently long the object can generally be viewed by daylight or lamplight such as can be made to fall on it without any special aids and, when desirable, the lighting can be improved by placing in front of the microscope a Bull’s Eye Condenser (No. 13.9250, p. 110). This applies to low power objectives up to HH, say. With higher powers, from Objective B upwards the working distance is too short to admit of direct illumination from without, and in all these cases it becomes necessary to illuminate the object by light passed through the objective. This is accomplished with the aid of a Vertical Illuminator.
No. 11.0400. * Vertical Illuminator (Fig. 15). The mount of the apparatus has at the side a window, through which the light proceeding from the lamp falls upon a reflecting prism covering half the aperture of the objective. Undergoing total reflection at the oblique face of the prism, the light traverses the objective and is thus concentrated upon the object. It will be understood that the presence of the Vertical Illuminator does not encroach upon the field of view.
To secure the best results while using the Vertical Illuminator it is most essentialthat the back lens of the objective should approach the prism as closely as possible, and hence all objectives intended to be used with the Vertical Illuminator should be fitted with specially shortened mounts. This does not interfere with their use for ordinary observation, provided they are not specially corrected in other respects. As a rule, objectives so mounted are corrected for a mechanical tube-length of 190 mm. When setting the draw-tube, the depth of the Vertical Illuminator should be deducted from this length, assuming the illuminator to be attached to the tube without any intermediate adapter.
Objects mounted under a cover-glass cannot be viewed through the Vertical Illuminator with dry lenses owing to the reflection of light which occurs at the cover-glass and in this case it will be necessary to use an oil-immersion lens to obviate the ocurrence of reflection. As a general rule objects so viewed should be uncovered, which again necessitates all objective of higher powers from the Apochromatic 8'mm Objective and the Achromatic D Objective upwards being specially mounted for the absence of a cover-glass. Objectives so adjusted cannot, of course, be used for examining objects mounted under a cover-glass in the usual way. It is always advisable to cut down the pencil of light which proceeds from the lamp until it just covers that portion of the object which can be seen through the objective. This can readily be accomplished by illuminating the object with the aid of a bull’s eye lens fitted with an iris-diaphragm. Suitable incandescent gas lamps and electric glow lamps are Items Nos. 13.9200 and 13.9210 listed on page 110.
Full particulars respecting the management of the Vertical Illuminator are given in the Directions, Mikro 89.
No. 12.0410. NACHET’s Vertical Illuminator with Iris Diaphragm. In its general arrangement this illuminator resembles No. 12.0400, from which it differs only in that the window at the side is fitted with a small iris-diaphragm. This serves like the iris-diaphragm of the ABBE illuminating apparatus to limit the aperture of the illuminating pencil.
No. 12.0450. BECK’s Vertical Illuminator with Iris Diaphragm (Fig. 16). This Vertical Illuminator has the reflecting prism replaced by a plane glass inclined at an angle of 45° to the axis of the microscope. This arrangement has the advantage that it leaves the entire aperture of the objective free for observation, in consequence of which it is preferable for observations under a high magnification in that it does not interfere with the resolving power of the objectives.
The vertical illuminator used on this microscope utilizes a prism and corresponds to No. 12.0410, Nachet's Vertical Illuminator with Iris Diaphragm..
Note that the mirror mounted at the side can be used to reflect the light source into the vertical illuminator. In this particular case from the user's perspective,
the source would have been located at the front left of the microscope. The side mirror is double sided with the concave side facing the illuminator (hover over the image).
The Zeiss archive states that
No. 76536 is stand ISB with the large stage. It was
delivered to Karl Wetzel, Masch. Fabr., Gera-Reuss in 1920.
It was equipped with the objectives 16.0/0.30 and 4.0/0.95
("kurz gefasst") which still remain and the eyepieces 4 and 8. Evidently, additional eyepieces were added later.
The machine factory and iron foundry, Karl Wetzel Maschinenfabrik, was founded in
Gera Germany in 1877. In 1936, that company merged with
Union AG in Chemnitz, but was later separated after WWII. Nevertheless, the company's descendant survived and is still in existence
as UnionChemnitz. See this brief history of the firm.