A mysterious field microscope - the Chinese TWX-1 (II)
We are going to continue our review of the tiny Chinese military field microscope.
An efficient electrical light source is important for practical field work and most
older instruments cannot compete with modern LED microscope light. The TWX-1 performs better.
The primary light is a small common filament lamp driven by a modest voltage (two AA batteries).
Nevertheless the light is ingeniously guided through a movable mirror, iris, blue filter and condenser.
As a result we end up with a brightly and evenly illuminated field of view.
Chinese field microscope TWX-1, with open "boot lid".
You will be able to see the two mignon (AA) batteries and a spring-loaded milled knob
which serves to move out a slider (!) with the 15x spare eye-piece. The eye-piece
is fixed by means of a thread. Overall it is a remarkably professional build quality.
No noise, everthing fixed tightly in appropriate position.
In order to achieve a small volume (14 cm x 11 cm x 5 cm)
the light path had to be folded three times above the stage as can be seen on the following photograph:
Light path (schematic): the TWX-1 light path is folded several times above
the specimen table. As a result the specimens can remain upright as in an ordinary light microscope.
Now we will follow the light path from the bulb
to the eye-piece. The bulb is situated in a massive metal housing behind a hinged lid
and peaks through a glass lens.
Front view of the TWX-1, as seen from slightly below:
Cast metal base plate with rubber spacers and hinged lid of bulb compartment (1)
The only decoration (?!) on the military instrument: concentric rings on the backside of the fully movable concave mirror (2).
Second thought: no decoration, just enhanced stability ...
Lever (3) with tiny blue (bulb light correction) filter.
The condenser (4) could be adjusted in height and fixed by a screw (but it is in fact working fine with all three objectives,
without any adjustment).
Specimen table (5), moveable.
everything made of metal.
There are many tedious threads in the web, how to upgrade
a microscope with an LED illumination. In case of the TWX-1 it is really simply.
Just buy a (threaded) LED bulb replacement, screw it in place and do not hesitate to
dim the tremendous power by means of a piece of handkerchief.
But keep in mind that the old-fashioned bulb will be able to perform the job as well,
though possibly not as long - so you might as well stick to the original illumination
thus preserving the authentic character of the 1970s.
A modern threaded LED might replace
the classic filament bulb. The photograph depicts a perfectly fitting TerraLUX TLE-1S
(on the left side) but other products might work in a similar manner.
The remaining light path can be deducted from the following series of photographs.
TWX-1 with illumination switched on. The bulb is situated
in a massive metal housing.
All optical elements are positioned in an extremely condensed manner,
nevertheless the mirror can be rotated as needed. No collision between filter, condenser, mirror and
The filament is mirrored onto the blue filter
thus mimicking the perfect illumination of an "upgrown" instrument. As a consequence
the electrical power is being used very efficiently even though the voltage and minimal working current
are amazingly modest.
In the next step the light rays are passing
through the small iris and condenser systems.
Partially dismantled: two 90° prisms for light guidance.
The one on the objective side can be adjusted when necessary.
A further prism (180°) is situated at the rear side, below the eye-piece.
Of course, we have to look at the tardigrade specific performance as well:
TWX-1 demo photomicrograph: egg of a Macrobiotus sp. tardigrade.
Diameter with protrusions 92 µm, without protrusions 82 µm.
Permanent preparation in Hoyer's medium. Please note the egg-cup-shaped protrusions as
mentioned in literature. The height of those tiny protrusions, really delicate structures, is about 5 µm,
their top diameter ca. 2 µm. In case somebody should be interested - here
are some more technical data: objective 45x/0.63. Camera Nikon Coolpix 995 (3 true megapixels :-),
adapted by means of a "Coolpix" (CP) wide-angle eye-piece adapter from a well known Indian microscopy provider.
In the next issues we will have a closer look at the
three tiny (non RMS) objectives and discuss their performance on the basis of classical test diatoms.
© Text, images and video clips by
Martin Mach (firstname.lastname@example.org).
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