Zeiss Stereomicroscope III
I have owned this legacy stereomicroscope for several years. I do not use it for photomicrography because I have better equipment for this purpose, but I find it convenient to have a simple stereomicroscope of good quality at hand for quick examination of three-dimensional subjects in incident illumination.
In my daily work as a paleobiologist, for several years I used a simple Olympus SZ ("just SZ") stereomicroscope in hammered-gray paint. This was the original finish chosen by Olympus at the launch of this model in 1961, and was subsequently changed several years later to what Olympus calls "ripple-pearl", i.e. a more non-descript, slightly amber-toned gray. This is said to be the first Japan-made stereomicroscope, and remained in production for quite a long time. Actually, while working in Japan I saw and used one or two legacy Olympus stereomicroscope models that might be even older, but probably were never exported to the West.
When I switched career from science to the software and telecom industry, I decided to equip a personal lab at home, in part to continue my research in paleobiology in my scarce spare time, and in part with the long-term goal of having a reasonably well-equipped lab in which to spend plenty of time after retiring. I did not particularly miss the Olympus SZ, and for a few years I made do with a PZO MSt 130 stereomicroscope made in communist Czechoslovakia, one of several clones of the pre-World War Two Zeiss SM1. I remember that the image given by this stereomicroscope was sharp but had a slightly yellowish cast (possibly caused by yellowing lens cement, or perhaps by the use of thorium glass, which may become yellow or brown with time because of radiation emitted by radionuclides in the glass).
Eventually I decided to sell the PZO scope and bid on a Zeiss Stereomicroscope III on eBay. At the time, I was equipping a Zeiss Photomicroscope II, and it felt natural to choose the same brand for my "new" stereomicroscope.
I already had some experience with Zeiss stereomicroscopes, like the Stemi DV4, made largely of plastic, and knew enough to avoid them like the plague. I decided therefore to go back in time a few generations of scopes to get a more solidly built one, as well as to get more for the money. I had hands-on experience at work also with the Stereomicroscope II, which I did not really like and was not interested in purchasing.
My first attempt was a failure. The Stereomicroscope III I received had been described by the seller as "in good condition" and looked externally acceptable (except for having only one eyepiece, a Zeiss with barrel made entirely of plastic), but its internal mechanisms were heavily rusted and corroded, and much of the zoom optics smashed to small bits. It may have fallen overboard into the sea, and afterwards fished out and wiped dry externally, but no attempt was made to drain and clean it inside, probably because the smashed optics made the scope useless in any case. Luckily it was cheap, and I could reuse the stand, focuser and a few other parts.
My second attempt went better, and I am still using this scope.
This Stereomicroscope III came equipped with Nikon eyepieces (which work well on this scope, have diopter adjustments, and have a higher eye relief than some of the original Zeiss eyepieces) and a base originally designed for transmitted illumination via a convex mirror mounted on an under-stage platform (only the post of the mirror is shown in the figure). This platform works for me as a specimen holder for incident illumination, after removing the mirror. The white central area of the disk is integral with its black rim.
The original specimen holder platform was mounted on the column of the scope a few cm above the mirror, and the whole scope was a bit too tall for comfortable use on an office table and with a normal office chair. If transmitted illumination is needed with this scope, it is better provided by a thin LED iluminator placed on the base.
The round disk on the base shown in the picture is interchangeable with the disks seen in other Zeiss devices, like the Tessovar. These disks have a set of holes around their periphery to house retaining clips, have a central insert of smaller diameter than the white disk shown in the figure, and may therefore be less suitable for large subjects. The most common insert is made from painted aluminum, with one white and one black side. There is also a glass insert of the same size, used for transmitted illumination.
Like all Zeiss West (but not Zeiss Jena) stereomicroscopes of the mid-20th century, the Stereomicroscope III is of the Greenough type, with two independent optical paths and objectives (although it can use a single additional objective). Unlike the Stereomicroscope II, which rotates an internal drum to get a few fixed magnifications, the III is a true zoom scope. The magnification knob has stiff and noisy detent clicks at 1x, 1.2x, 1.6x, 2x, 2.5x, 3.2x and 4x, but the zoom mechanism can also be set at intermediate positions. The magnification scale is only present on the right side knob. This magnification must be multiplied by the eyepieces´ magnification (typically 10x) to yield the total magnification of the scope. It might be possible to disable the detent mechanism, but this requires at least the knobs to be removed, which my scope resisted. There is also a risk that the magnification accidentally shifts on its own during use of the scope, once the detents are removed. In the end, I decided to live with the detent clicks.
Note - I have seen illustrations of specimens of Zeiss Stereomicroscope that correspond in all details to the Stereomicroscope III, except for being painted in hammered greenish-gray color. These specimens were sometimes identified by their sellers as Stereomicroscope II. However, I have seen a manual for the Stereomicroscope II, and it has a photograph of the non-zoom scope on the cover, so there is no question in my mind that the zoom model in hammered paint is instead an early Stereomicroscope III.
Although both lower and higher magnification eyepieces than 10x are available, I find them essentially useless. Lower magnification eyepieces have a narrow field of view, while the only reason to use them would be to get a wider field of view than 10x eyepieces. Higher magnification eyepieces have a low and narrow exit pupil and are difficult and eye-tiring to use. The body of the scope has a conical bayonet at the bottom that accepts an additional objective to change the magnification range. This is a better way than eyepieces to change the magnification range of the scope. However, these objectives are hard to find on the second-hand market, and since multiple Zeiss scopes use the same bayonet it is difficult to decide which scope model a given objective is designed for.
The body of the Stereomicroscope III can rotate within a ring, which is attached to the focuser mechanism. Neither the Stereomicroscope II nor the Stemi IVb have such a ring.
The focuser shown in the above figure has an unusually long rack with a travel of over 15 cm. The lower part of the travel is too close to the subject stage to allow focusing, but may be useful when storing the scope in a box or cupboard where vertical space is limited. With reasonable care, this stand and focuser last essentially forever. There is no fine focus knob, but given the relatively low magnification this is not really necessary.
This stereomicroscope is usually equipped with one illuminator mounted on an articulated arm attached around the bottom end of the microscope body. There is actually space here for two arms (and therefore two independently orientable illuminators). The incandescent bulb of these iluminators is obsolete, and the whole illuminator is better replaced by a simple LED spotlight, preferably dimmable. The above figure shows two original Zeiss illuminator arms, but the illuminators I use are not original (they consist of little more than a LED and small heatsink), and therefore I am not showing them in the figure.
Other Zeiss Stereomicroscope models and related equipment
The Zeiss SM1 is an early Zeiss stereomicroscope designed just before World War II. It is painted black and the body is characterized by its angular lines. Magnification is changed by rotating a horizontal internal drum, much like the Stereomicroscope II. The SM1 was subsequently copied by PZO (the MSt 130 shown above), Zeiss Jena (Citoplast and other model designations) and Lomo (MBS-1).
The Stereomicroscope Ib has a horizontal drum with three objectives, and the same ring to rotate the microscope body as the Stereomicroscope III. The Stereomicroscope Ib may actually have been produced until a later date than the Stereomicroscope II. The Stereomicroscope Ib and II do not have a zoom mechanism, which somewhat reduces their versatility compared to subsequent models. On the other hand, this also means that these non-zoom models have fewer mechanical parts that can break or misalign. Their optical quality may be a little lower than the Stereomicroscope III, especially when used with the original eyepieces that lack diopter adjustments.
The Zeiss Stemi/Stereomicroscope IVb is a slightly later model than the III, with a longer, barrel-shaped body and a similar zoom mechanism as the Stereomicroscope III, but sporting large magnification wheels like the Stereomicroscope II and providing a higher zoom range (0.8x to 5x) than the Stereomicroscope III. One further difference is that the body of the Stemi IVb does not rotate within a ring, unlike the Stereomicroscope III. The Stemi IVb used the same stands as the Stereomicroscope III and Tessovar, and both Stereomicroscope models are compatible with several Zeiss OPMI (Operations Mikroskop, i.e. surgical/medical microscope) heads and stands. Sometimes the Stemi IVb is equipped with a motorized focuser. Do not confuse the Stemi IVb, which is as solidly built and durable as the Stereomicroscope III, with the more modern, largely plastic and easily broken Stemi DV4.
More modern Zeiss stereomicroscopes use different stands and focusers, incompatible with the Stereomicroscope series. Most of these modern models, unlike the Stemi DV4, are well made but very expensive on the second-hand market. There are also several stereomicroscope models made by Zeiss Jena. At least some of them are said to be well-made and durable, but I know near to nothing about them.
The Zeiss Tessovar is designed for use in photomacrography, and has a zoom magnification changer (plus a four-position objective turret with custom objectives) and a single optical path. It shares some of the accessories, especially stands, focusers and illuminators, with the Stereomicroscope III and Stemi IVb, and clearly was designed and manufactured roughly at the same time. The optical design of the Tessovar zoom is also very likely derived form stereomicroscope optics. Note however that the Tessovar cannot use the binocular heads of the Stereomicroscope, Stemi and OPMI series, and instead can use some of the photo tubes for the Universal and Photomicroscope series. Like the Stereomicroscope III, the Tessovar is equipped with a ring that allows rotation of the scope body.
The Zeiss Stereomicroscope III is a good compromise between solid and durable construction and flexibility of use. If you need a stereomicroscope for visual observation only (not photomacrography) from 10x to 40x and for use mostly with incident illumination, this model is better value for the money than more modern models from, e.g., AmScope, Swift, no-name China-made scopes, and even some of the more modern Zeiss scopes.