The Minimum Microscope

The Hensoldt Tami

by Martin Mach, Munich, Germany


 

There are a number of papers about unusual microscopes in Micscape which are a real pleasure to read for everybody interested in this field. I would like to contribute one more paper to this group, about the historical TAMI pocket microscope.

The Hensoldt company

The German company Hensoldt in Wetzlar, in comparison to some famous British microscope manufacturers—a rather young company, was founded by Moritz Carl Hensoldt in 1852. Early microscope catalogues included many different types of compound microscopes, oil and water immersion objectives and several dissecting microscopes. In particular, Hensoldt binoculars and spotting scopes soon had a worldwide reputation, though the company never reached the fame of its big brothers Zeiss and Leitz.

There had always been some parallel production of optical instruments for the German army. For obvious reasons military production decreased drastically after the First World War. As a consequence, the Hensoldt company decided to return to its microscopical tradition. In 1920 a new product line of field microscopes was launched starting with the Tami (i.e. Taschenmikroskop, pocket microscope). In 1928 the Hensoldt share majority was taken over by Zeiss but at least some part of the Hensoldt products were still sold with the Hensoldt trade mark and even today there is still a Hensoldt group within the Zeiss company. The Tami pocket microscope and its successors have been widespreadly used among German microscope amateurs, also after the Second World War.

Features of the Tami microscope

The Tami (see fig. 1 and 2) is an extremely small compound microscope for incident and transmitted natural light. The very small concave mirror for transmitted light is sealed in a flat cylindrical metal base with a glass cover on top of it (the stage). The mirror base can be rotated to adjust the illumination and can be removed for investigations with incident light. Two extractable, straight tubes zoom the magnification from 35x to a maximum of 225x. Focusing is done with concentrical tubes linked by a thread. The front lens of the single objective is removable for low magnifications, the eyepiece threaded into the tube. A massive brass cover which can be threaded on the base serves as a transport protection for the microscope. Fig. 3, an illustration taken from the Hensoldt catalogue, shows the Tami mounted on the optional additional support.

For those who are interested in technical details I have compiled some more data in the two tables below.

Table 1: Optical and mechanical features

Magnification zoom range from 35x to 225x
Change of magnification by means of two stage telescopic tubes (and via removal of front lens) with variable tube length from about 70 mm to 160 mm
Magnification reading markings at the outer side of the tubes in spacings of 5
Focusing focusing with thread in concentric tubes 1 mm per turn
Objective achromatic, with removable front lens, no inscription

non-RMS thread

magnification about 15 x with N.A. about 0.30 or better

outer diameter of thread 21.5mm

Eyepiece fixed non-standard eyepiece magnification ca. 15 x
diameter of eyepiece tube: 20 mm
Field of view at magnification 35 x
at magnification 225 x
ca. 4 mm
ca. 0.6 mm
Mirror concave mirror on a small inclined socket in the sealed metal base. The base can be rotated in the base mount around the z-axis in order to adjust illumination diameter of mirror ca. 1.4 cm
Electrical illumination accessory  
Condenser none  
Diaphragm none  
Filter-holder none  
Stage circular, on the removable circular mirror base made of a flat cylindrical metal body with glass cover.
Frosted ring as center mark. One removable "U"-shaped iron clip for standard slides
diameter of removable base: 3.6 cm
diameter of usable stage (including base mount) 4.25 cm

diameter of frosted ring: 9 mm

 

Table 2: Dimensions, weight, material, inscription and prices

Dimensions max. height of microscope stowed away with cover 10.3 cm
  max. height of microscope in use (with both tubes extracted) 19.5 cm
  min. height of microscope (with tubes retracted) 10 cm
  max. diameter incl. cover 4.6 cm
Weight weight of sealed base with mirror socket and glass stage 75 g
  weight of body with tube, optics, base mount and stage clips 234 g
  weight of cover 137 g
  overall weight 446 g
Materials base brass and another copper alloy, probably tin bronze, both covered with black coating, glass cover on top
  body copper alloy, probably tin bronze with black coating
  tube and objective nickel-plated brass
  focusing tube aluminium alloy with black coating
  cover brass, black coating
Inscriptions on top of cover 7964 (serial no.)
HENSOLDT
WETZLAR
  on focusing tube Hensoldt
Wetzlar
D.R.P. a.
  on eyepiece Tami
Prices of Hensoldt microscopes (1933) in German marks TAMI 45.--
  Electrical illumination 10.--
  Additional stage (fig. 3) 10.--
  Top of the line PROTAMI 230.--
  Simple bench microscope 103.--
  Top of the line bench microscope 657.--

 

Performance and usability

The image below (fig. 4) has been taken by means of a cheap CCD computer camera through the tube of the Tami microscope at maximum magnification. The eyepiece and the camera objective have been removed for the photograph in order that the light could pass through directly from the microscope objective to the surface of the CCD chip. The largest diatom on the picture measures about 200 microns in diameter. Please note that the structures on the smaller, dark diatom on top of the image are clearly resolved. The light source used was standard daylight (inside a room at 9 a.m.). Though there is no condenser, no diaphragm whatsoever and no matte filter you still get the most important details and a reasonable overall image quality. And please keep in mind that this microscope is about 70 years old and just peppermill sized.

The surprisingly even field of view of the Tami doesn't quite reach from left to the right, but is still much better than those formidable 'light at the end of the tunnel' constructions. The frosted ring on the stage is very helpful if you have to find an object on the slide quickly. You even do not have to carry along a slide as you can place the objects or a drop of water directly on the glass stage. So the Tami is ideal if you do not want to carry along a lot of equipment, when you are at the beach or when you just want to screen some samples in order to decide whether it might be worthwhile to take them back at home.

If you are among those people who like to discuss the ergonomics of office furniture and computer screens you will certainly dislike the Tami because of its straight monocular tube, its tiny size, its relatively slow focusing screw and so on ... On the other hand the Tami still today can serve as a really undestructable companion outdoors. The massive rigid metal cover (30% of the overall weight) will perfectly preserve the instrument in many situations which the microscopist probably would not survive. But do we really like this idea?

By the way, the contemporary bigger and much more expensive Hensoldt pocket microscopes METAMI and PROTAMI came with iris diaphragm, adjustable condenser, tripod thread, objective revolver, oil immersion objective (N.A. 1.34), removable double mirror, removable stage and many other thrilling features. But one should not mix this in one paper with the ingenious and still usable simplicity of the Tami microscope.

Comments to the author Martin Mach welcomed.

 

Images (photographs by the author).
Click on images to view larger ones. Use browser back button to return to article.


Fig. 1: The Tami microscope on the photograph (serial no. 7964) shows signs of heavy use but is still in perfect optical (though perhaps not visual) and mechanical condition.


Fig. 2: The three main components: base with small mirror and stage, cover and body with optics.


Fig. 3: The Tami microscope as shown in the Hensoldt 1933 catalogue with mirror base removed and optional support fixed to the body.


Fig. 4: Photograph taken with CCD camera through the Tami pocket microscope at maximum magnification. The large diatom on the left measures about 200 microns in diameter.

 

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