Magnifiers: a closer look (III)
The all-in-one magnification promise

There is a serious long-term tradition of folding magnifiers with two or more magnifications, going back at least 200 years. Just as one of many examples, fig. 1 is depicting an item of this kind: an "Enuro" (i.e., Eschenbach, Nuremberg) 10x/20x folding magnifier. Normally you will be using the 10x optics, but there is still a little bit of reserve for boasting among colleagues and for slightly enhanced detail resolution.

Fig. 1: "Enuro" folding magnifier with 10x/20x magnification. Metal housing with two two-lens (i.e. doublet) systems. Not achromatic but delivering an acceptable overall performance. Estimated age: ca. 60 years.

The wish to own a little bit more of everything is definitely characteristic for the human species - just think about the tale of the fisherman and his wife. And, perfectly true as well, also airplanes and computers wouldn't exist without this wish to be more and to own more.

In 1972 Arthur Seibert delivered a German patent request (DE19722219203) featuring a new pocket magnifier. It came with 4 optical heads which can be combined in various ways, thus providing 8 (!) different magnifications. Besides, this magnifier concept called OCTOSCOP®L boasts with a beautiful, symmetrical design.

Fig. 2: The Octoscop by the Arthur Seibert company (EMO) in Wetzlar, Germany. This company is also well known for its 5x photographic magnifier, called Macromax and the tiny Emoscope (Emoskop), a miniature microscope-telescope combination. The Octoscop features achromatic glass lenses in a plastic housing and weighs 25 g. It measures 8.1 cm x 3.2 cm x 1.6 cm and came with a dedicated slide-in container made of leather.

The four optical heads of the Octoscop are as follows:
--  2x – plan-convex single lens
--  4x – plan-convex single lens
-- 10x – cemented achromatic doublet
-- 18x - partially cemented achromatic triplet
The optical heads can be combined in various ways in order to deliver the full range of magnifications (2x, 4x, 6x, 10x, 14x, 18x, 20x and 28x).

Fig. 3: The backside of the Octoscop with two magnification reading windows. In this situation they are empty - but they will come up with numbers as soon as the cross arms will be in a parallel or anti-parallel alignment.

Fig. 4: The Octoscop in parallel orientation. Now the windows are signalizing the respective combined magnification readings: 6x (made up of 2x plus 4x) and 28x (made up of 10x plus 18x).

Fig. 5: The Octoscop in anti-parallel orientation. The windows are signalizing the respective combined magnification readings: 14x (made up of 4x plus 10x) and 20x (made up of 2x plus 18x).

The following pictures are documenting the various magnification effects. Please keep in mind that the typical tardigrade body length is about the same as the height of a number "1" in the production year number on an European 1 Cent coin (0.65 mm). Let's begin with the twofold magnification:

Fig. 6: 2x is a rare magnification for folding magnifiers, kind of reading glass. As to be expected the field of view is huge, ca. 7 cm. But be warned that this magnification is not very useful for your tardigrade studies! The diameter of those coins is ca. 16 mm.

Fig. 7: The 4x magnification, as well not too common in the world of folding magnifiers. But now the year number is visible as a whole, still not clearly readable. This magnification might be used in order to check a medium format transparency on a light desk.

Fig. 8: The 6x magnification. You might be able to decipher its reading "2015" now.

Fig. 9: A bigger step towards readability and usability - the 10x magnification. This is the most common standard among pocket folding magnifiers, e.g. abundantly used in the classification of diamonds. The fine structure of the coin with its typical tiny flaws and usage signs is beginning to appear.

Fig. 10: A further exotic magnification - 14x. Now the 16 mm diameter of the coin is almost filling the field of view.

Fig. 11: A further exotic magnification, namely 18x. It is providing an idea about the tinyness of typical tardigrades (same as the height of the number "1"). This is one of the best usable magnifications of the Octoscop, with a still comfortable object distance of 13 mm.

Fig. 12: The 20x magnification is definitely disappointing: now the working distance is shrinking dramatically to 5 mm (!). Due to this object vicinity the 32 mm diameter optical heads (a combination of 2x and 18x) are overshadowing the object. Furthermore, disturbing reflections are becoming apparent.

Fig. 13: Finally, the so-called "28x" magnification. It has the same problems as the 20x constellation, now with 4.5 mm working distance, which is way too low for practical usability. Moreover, in this constellation the instrument is definitely feeling bulkier and less usable than other magnifiers in the same magnification class.

In the next issue we will compare those results with the performance of a classical stereo (dissecting) microscope and a high grade single magnification folding magnifier. This will help to demonstrate the optimum performance design for a high power handheld magnifier.

Resume: the optical quality of the individual Octoscop lenses appears to be above average. They are made of glass and their finish looks perfect. Furthermore the Octoscop is offering a wide range of magnifications in a single instrument and its lens combinations appear to be perfectly usable up to 18x. Besides it is a highly collectible item, with an impressive design.

Nevertheless the "universal" character of the system bears its drawbacks as well. In particular the 20x and 28x magnifications are becoming victims of the sleek design: their mechanical overlay with two relatively big lens housings is resulting in more-than-necessary low working distances and blocking natural light.

Besides, as will be shown in one of the issues to come, single lens magnifications of high-power overlay combination magnifiers do not simply add up like (10x + 18x = 28x) but result in drastically lower magnification values. Moreover, our own measurements are indicating that the maximum magnification value of the Octoscop is close to 20x, thus ranging far below its 28x specification.

© 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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