The bin shed roof (II) or: the blue backside

Some facts are definitely easy to understand, but definitely easy to overlook and forget as well. As most of you will know, we had been almost exclusively using the Russian MBS-10 stereo microscope for the screening of our tardigrade petri dishes: April 2012,  May 2012 und June 2012).

One of the biggest advantages of the MBS-10 is its huge working distance of ca. 10 cm. On the other hand we should be aware of the fact that high microscopic resolution will always be based on a rather low working distance. Admittedly, there are some exceptions, e.g. so-called long distance objectives but as a rule we must approach our objects in order to gain maximum detail information: the respective objects are sending light rays in all directions and in order to catch all those rays, including the most oblique ones we must be as close as possible. This is the concept of numerical aperture (the angle of view which can be reached by a given objective).

Coming back to our MBS-10 we must accept that this instrument is primarily designed for comfortable preparation work and a large field of view. But, as there is always a trade-off between working distance and resolution we have to accept that maximum resolution cannot be the strong point of the MBS-10 microscope,

In order to illustrate this we will have a look at one of those old-fashioned stereo microscopes with interchangeable conical objectives of different aperature (different magnification):

Fig. 1: So-called Echiniscus "tun" as found on the bin shed roof (cf. most recent magazine issue). The illumination is performed by a blue tinge LED flashlight. Length of the tun: 0.12 mm.
Image taken by means of a Meopta G11P Greenough stereo dissecting microscope (fig. 3), with its 10x objective.
Technical annotation: The small standard diameter eye-piece tubes of the Meopta microscope allow a simple, not brand-specific camera adapation as described in July 2019.

In order to provide a rough idea about the respective tardigrade size relation we are providing a photomicrograph showing the date numbers on a European 1 Cent coin (0.65 mm in height). The tardigrade tun shown in fig. 1 would neatly fit into the upper cavity of the "8".

Fig. 2: Detail view (slightly oblique) of the date on a European 1 Cent coin. Image width ca. 0.7 mm. Photographic framework as in fig. 1 (Meopta G11P stereo microscope, with its 10x objective).
Some fine structure can already be perceived on top of the figure "8". The degree of detail resolution shown can easily be equalled by a standard microscope's 10x objective. But it must be kept in mind that this image is merely representing a flat snapshot of the real visual stereoscopic impression as seen through the stereo microscope. Overall, this instrument is quite competitive and it may serve as a proof that you do not necessarily need a microscope produced by one of the "big four" (Leitz (Leica), Nikon, Olympis, Zeiss).

The Meopta G11P stereo (dissecting) microscope as shown in fig. 3 was offered on Ebay for a moderate price (ca. 100 US $). Even though its design might remind us of a stork after a car accident, it is a perfectly working instrument - and it can be adapted to a wide range of tasks. It has a mirror which will provide transmitted light and dark field, plus, of course, simple incident light which can easily be delivered by a bargain IKEA "Jansjö" led lamp. Moreover its stand allows multiple variations, e.g. to direct it towards a flat vertical wall or to inspect some kind of kingsize rock specimen.

Fig. 3: The vintage Meopta stereo (dissecting) microscope with the 10x objective fitted to its nosepiece. Fig. 1 and fig. 2 were produced by this setup. The instrument came with a black-and-white plus a transparent object plate. We think that the image quality achieved with the 10x objective can easily compete with many nowadays "zoom" stereo microscopes. Once again this is not so much due to optical manufacturing quality but to a well-suited, low working distance.

Fig. 4: This objective box came with the Meopta stereo microscope. It contains four pairs of objectives marked as 2x, 3x, 5x und 10x.

To sum up, this is a highly useful instrument but not for use in a beginner's environment. In order to reach optimum results the users will have to learn and understand the pros and cons of the various objectives, the wide range of illumination variants and the flexibility of the stand.

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
The 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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