Small take-along helpers: Loupes (II)

In the last issue we had a closer look at the anatomy of an optically well corrected Steinheil type real triplet  loupe from Belarus . We will use it here in order to discuss the usability of a typical high quality 10x loupe for tardigrade studies. Of course there exist many other excellent 10x loupes by other makers as well, but please beware of those myriads of Ebay vendor driven pseudo-"triplet" deceptions ...

Steinheil type loupe from Belarus. Weight: 40 grams. Dimensions: 35 mm x 27 mm x 25 mm.

Okay, now let's imagine you were travelling to a distant country for tardigrade studies just with this nice Belarus loupe, no additional eqipment. What would you be going to see?

In order to better clarify the potential power of a 10x loupe we have "composed" a highly condensed, simple scenario with many tardigrades and only little moss. The tardigrades were carefully transferred to our  micro aquarium. As seen through our Belarus loupe the visual impression is as follows:

View through the 10x Belarus loupe on a cylindrical water column with a diameter of 0.45 cm and a height of ca. 2 mm. Complete viewing area.

When concentrating intensively on the center area we will perceive the artificial tardigrade scenario as shown below - none of the characters could be safely discerned with the bare eye:

"Felt" image as seen through the 10x loupe. Droplet area diameter 0.45 cm.

Thanks to the 10x magnification we are able to recognise the various actors in the micro aquarium:

1  Milnesium tardigradum, crawling on a small moss plant.
2  Medium sized Heterotardigrade (Echiniscus sp.).
3  Small Eutardigrade, with orange intestine content.
4  Medium sized Eutardigrade, ventral view.
5  Eutardigrade and very small Echiniscus tardigrades, in close vicinity.
6  Medium sized Eutardigrade, with green intestine content.
7  Big Echiniscus tardigrade, moving vigorously.
8  Big Echiniscus tardigrade, pausing.
9  Two tardigrade eggs, diameter ca. 65 µm (0.065 mm)

Though this sounds like a success, in particular when keeping in mind the price of nowadays 10x loupes, it is a situation of disillusionment as well. Even with a very, very modest microscope we would perceive much more detail. Just have a look at the following image of the pair of eggs (marked as "9" above) taken through a 20x microscope objective and a 10x eye-piece:

Tardigrade eggs as seen under the ordinary compound microscope - what a difference to the loupe!

The sellers of loupes will claim that magnification is not as important as actual image definition and resolution. In fact, already a high quality 3x loupe can provide stunningly crisp images and can turn out as an extremely useful tool when e.g. soldering small electronic parts or when looking at some of the bigger bugs and plants in nature. For many tasks in everyday life a good 3x loupe is the optimum dedicated viewing device, a 10x loupe often might be stupid over-kill and silly money in those applications - in so far the vendors are perfectly right.
But the tardigrades, as we all know, are somewhat special. A good optical quality alone might be not sufficient in this case. Why? You see, the bare eye is able to resolve two points when they are at least 0.12 mm apart. This means that for the eye a 0.2 mm tardigrade will appear as a two pixel object at best. With a 10fold loupe this multiplies up to 20 pixels which is still a very poor image size, like the Windows® hour glass icon. There is an inevitable conclusion:

A 10fold magnification as a rule will be not enough for our tardigrade studies!

There exist (fewer) loupes with higher magnification numbers than 10x. We have already pointed out in the last issue that optical disadvantages go hand in hand with the higher magnifications: small usable lens diameters, small field of view, need for additional (artificial) light, small focus depth, short working distance and the need for an extremely clean parallel orientation of the lens and the object area under investigation.
By the way, do you know why some older loupes are equipped with mysterious holes in the mounts (as shown in the last issue)? Here is the answer: they will help to achieve a perfect parallel orientation of lens area and investigation area. Have a look at this:

Loupe stand in combination with an ordinary folding loupe providing optimal viewing geometry, which is urgently needed for higher loupe magnifications. Illustration from Henry Scherren's book "Through a Pocket lens", London 1897.

Dr. Hager's small dissection microscope, though still a rather cheap and humble instrument, comes already a little bit closer to the "big brothers and sisters" (the true dissecting microscopes):

Hagers small dissecting microscope "Präparirmikroskop", ca. 1880.

Those two instruments shown above are small and ingenious but there is a fatal disadvantage: it will be difficult to get hold of them today.
So we will have a look at two more recent devices. A fashionable but not cheap loupe is the "Betamag" folding loupe, which has an inbuilt stand as well:

"Betamag" folding loupe. High magnification (20x), as a consequence low working distance.
The lens can be adjusted by means of a focusing thread and a counter thread. It folds neatly under a solid chrome finished cover.

Too expensive? No, not terribly expensive. But, in case you want to spend little or no money at all, there are alternatives. In particular many first generation webcams do have excellent glass objectives with an extremely short focal distance (1 cm an less) thus providing a 20fold and greater magnification. Some of them even have a focus thread which comes in quite handy as you will have to find a very small "crisp focus slice" - fractions of millimeters turn out to be decisive in order to reach the optimum image quality.

A webcam objective to be used as a strongly magnifying loupe. Mount: Biycle bulb holder spare parts. This loupe is a nice and powerful ultra-miniature transmitted light loupe (e.g. to be used on a light box designed for transparencies).

In the next issue of the Water Bear web base we will check whether those more powerful loupes are actually able to provide an enhanced definition to be used for our tardigrade studies.

© 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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