A mysterious field microscope - the Chinese TWX-1 (III)

Like amateur-photographers amateur-microscopists have a tendency to meticulously scrutinize the technology of their instruments, and as a consequence are in constant danger to forget about the objects in front of the lenses.
Pure tech-talk can be fun, but we should always be aware that technical topics can be somewhat intellectually limited as well.

Our main concern in this issue is to illustrate that, though most technical refinements of microscopes might have originated in the western world, we do have remarkable eastern contributions as well. Nowadays all of us know that Chinese products can be very competitive. In addition, Chinese field microscopes have been very competitive already in the 1970s but the western world simply failed to notice. We are going to use a diatom test slide in order to demonstrate the excellent optical performance of our 1970s Chinese TWX-1 microscope.

Total view of a commercial diatom test slide - made by Klaus Kemp, U.K.; it contains classical resolution test diatoms as listed below:

1 - Gyrosigma balticum
2 - Navicula lyra
3 - Stauroneis phoenicenteron
4 - Nitschia sigmoidea
5 - Surirella gemma
6 - Pleurosigma angulatum
7 - Frustulia rhomboides
8 - Amphipleura pellucida

Please note that the resolving criteria (minute 'lines' and 'dots') are not visible in the total view.

In order to visualize the tinyness of those test diatom shells we are going to show the specimen slide in overview (full width of specimen slide), then pass on to the maximum macro mode of a good CCD camera:

Object slide containing the test specimens as introduced above. The massive lacquer circle has a diameter of ca. 1.1 cm, the inner circular confinement a diameter of only 0.3 cm. You will notice that the test diatoms are not visible at this low magnification. The photograph was taken by means of a Nikon Coolpix 995 camera which might be considered as technically obsolete today but is still able to deliver outstanding macro performance.

The same slide, as seen from a little bit closer, once again by means of the Coolpix camera. The diatoms are becoming discernible as a faint shadow, still barely visible. This photograph might serve as an example to define the borderline between "macro" and "true micro".

Please keep in mind that this is not a weakness of the Nikon camera which serves well in other, more moderate macro situations like in the depiction of a ballpoint pen tip as shown below.

Much easier to grasp by means of macro photography: The tip of a ballpoint pen. Camera: Nikon Coolpix 995.

Finally, unter the benchtop microscope, the diatoms are going to show their full frustration potential - for beginners, but also for professionals fighting against malfunctions of their microscope equipment.

(1) The fine striation of the faint Amphipleura pellucida [8] has to be classified as top-frustrating. It will become visible only by means of oil immersion and raking light.

(2) The "hexagon" impression of Pleurosigma angulatum [6] has been used extensively to teach beginners how to use the substage condenser in combination with a 45x/0.65 objective.

(3) The lines of Navicula lyra [2] are not as difficult and will be perceived with a good 10x/0.30 objective (the numerical 0.25 numerical aperture of the TWX-1 10x objective is not sufficient - no lines are visible in this case).

The objectives of the TWX-1 are really tiny, standing in close distance to each other:

The TWX-1 objective turret is really tiny, nevertheless it has interior stops (many bigger microscopes have outer stops).

The objective threads of the TWX-1 are made of brass.

The three TWX-1 objectives. For comparison (on the left side) a standard-size (and standard RMS thread) German microscope objective.

Well filled with optical glass: the 10x objective. Please note the tiny case of the 45x objective as well.

The TWX-1 45x objective is able to resolve the Pleurosigma angulatum test diatom, even though its specified numerical aperture of 0,63 ranges below the classical 45x/0,65 objective (with a numerical aperture of 0.65).

The 45x objective of the TWX-1 has no problems with the appropriate test diatom Pleurosigma angulatum: The dots are clearly visible. Photography by means of a "CP" (Coolpix) adapter - marketed by an Ebay seller from India - and a Nikon Coolpix 995 camera.

The 10fold objective of the TWX-1 shows good resolution but the flatness of its field is far from perfect. This might be an issue for those among you who like to screen perfectly flat cross sections. For the tardigrade microscopist it is no topic at all as the tardigrades are far from being flat. In order to provide an idea about the performance of the 10x objective you might have a glance of the following photomicrograph of a diatom circle prepared slide:

Diatom circle specimen, TXW-1 10x objective. The diameter of the circle is about 0.8 mm whereas the full field measures ca. 1,4 mm. As a consequence the not-too-good flatness of field doesn't become apparent on the photograph. Overall it is a fine image quality.

We will present a test image of the 90x objective in a future issue (on the basis of the really difficult Amphipleura pellucida diatom). We will work with unfiltered white light of a cheap TerraLux LED, without the recommended oil immersion of the condenser (i.e. with objective immersion only) and the old but reliable Nikon Coolpix 995.

Last but not least we are working on a small tardigradee sensation: at the moment we are testing a Tardigrade detector which will help to detect Echiniscus tardigrades in the field, without water immersion (!).
Up to now it has been impossible to quickly screen dry moss samples for tardigrades, and this will change. So, do not miss our next issue!

Literature

Frank Eric Round et al.: the diatoms. Biology & morphology of the genera. Cambridge University Press 1990.
[Annotation: lots of fascinating SEM images!]

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.

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