Small take-along helpers: Loupes (I)
A few years ago, in issue #24
we had presented some tardigrade image results produced by means of common,
vintage, low-budget lab microscopes. As a rule all those instruments will be
rather bulky and heavy, difficult to take along. As a consequence they will
be used at home only, in a quiet, low-light environment.
Antoni van Leeuwenhoek (1632 - 1723), the ingenious and famous Dutch
microscopy amateur, was far ahead of his time with respect to microscope miniaturization.
Up the the present day it remains unclear whether he actually made all his discoveries
with his tiny "travel-type" microscope or whether he might have owned
more sophisticated, bigger microscopes for stationary indoor use as well.
Now, which equipment might be useful for mobile
tardigrade investigations? No doubt that it should be small. How about a classical botanical
Magnification by means of reduced distance: loupes are devices
which permit the human eye to approach objects even to a distance of less than
25 cm - with the decisive advantage of keeping the crisp image (of course we could
approach the naked eye closely to the object as well, but this will result, as we all
know, in a blurred image).
Typical inscriptions on the loupes primarily indicate
the respective magnification (e.g. 28x, 20x, 15 x, 10x, 8x, 6x), in cases of
variable lens combinations the different possibilities (like "3x 6x 9x" on a loupe with
a 3x and 6x lens, where the single magnifications of the invididual lenses sum up
to the maximum possible magnification).
The variations among commercially available loupes are immense, in particular when keeping in mind those many international products fabricated since the 18th, 19th and 20th century. We are going to present a few images in order to illustrate this cultural diversity:
Loupes in plastic mountings with intense colours.
Left: a turquoise loupe from Taiwan with three identical plastic lenses, each with 5fold
magnification (thus reaching a 5x, 10x and 15x magnification). A nice
example for contemporary "retro" design (cf. the similar but historical
loupe with many identical features in the next image!). Length 6 cm.
Top: very old folding loupe (ca. 1880 - 1900) made of horn,
with three different lenses to be used in various combinations. Maximum magnification
ca. 20x, length 6 cm.
Classical 10x loupe, ca. year 1970. Baroque pre-war design, fine chrome finish. Optical system consisting of two separate lenses (Doublet), one plan-convex, the other biconvex. 50 mm x 30 mm x 22,5 mm. This system is commonly called aplanatic because two separate lenses perform better than a single lens with respect to spherical abberation. Free lens diameter 20 mm.
Rare Cloisonné folding loupe of unknown age. Biconvex single lens with 30 mm (!) diameter, 6x magnification. Rather big and heavy for a folding loupe (6 cm x 3,5 cm, 64 g). Nice example of a convergence from fascinating oriental design arts with occidental machinery-technical properties. Note the detailed cranes with green beaks and read caps, the beautifully ornamented side-wall decorations and the overall perfect craftswork with carefully rounded edges and reliable bolts.
Carl Zeiss Jena hand loupe with slightly conical handle. Overall length 15 cm. Extremely asymmetrical strongly curved bi-convex single lens with 3.5 cm focal distance, i.e. 7fold magnification. Lens diameter ca. 32 mm. Pre-war model made of plastic (Bakelite or Bakelite-like), glass and metall. Rather rare style mixture between the common hand magnifier and stronger "scientific" loupes. Houses in a fine "coffin-style" black cardboard box with wooden fittings and textile spacers.
Small classical Zeiss folding loupe in plastic mounting (8x).
At the time of its creation (1930s) in a fairly modern, straight-line design,
which appears to have been kept unchanged for many decades. Length ca. 3,5 cm.
Free usable lens diameter ca. 12 mm.
In front the respective Doublet optical system consisting of two lenses made of
different glass types thus providing excellent colour correction. A so-called
achromatic system. Very crisp and colour fringe-free image
quality until to the very edges of the field.
In contrast to mechanically mounting-linked lenses glued lens combinations are more difficult to recognise. In this case the borderline between the two glued elements becomes visible after some grinding:
Cross section through a glued loupe doublet lens systems.
One of the most successful classical loupe designs: True Triplet or Steinheil Triplet (see schematic diagram below), 10x, lens diameter 22 mm, "Made in Belarus". Don't hesitate to look out for this country on the world map! One of our favourite loupes. You will recognise two glue borderlines around the central bi-convex, slightly retracted lens. The only flaw of this product are the small fixing screws which exhibit a strong tendency to vanish, evaporate ... The good news: this screw escape is a rather slow process and your chances are good to get hold of them before they are definitely gone.
Steinheil-Triplet (schematic). Symmetric Bauplan consisting of three glued elements. In the center a biconvex lens made out of weakly refractive Crown Glass (normal glass) surrounded by two menisque type lenses made out of strongly refractive Flint Glass. Comparatively high production costs, excellent image quality.
Before switching to Ebay now in eager search for the magnificent
triplet system: be warned. There are many products with "Triplet" inscription which are
just named Triplet. This is similar to a motorcar which might have the name of
a tropical wind but is by no means identical with this tropical wind.
Many of those "Triplets" consist of a single biconvex glass cylinder
which will magnify as well but will never be able to provide the same image quality
as a true optical triplet system. Nevertheless you will be able to count the
number of bug feets with such a simple system as well.
This Triplet confusion might be only slightly or borderline fraudulent, in particular
when keeping in mind the prices of those pseudo-triplets. Moreover,
our Western term "triplet" will be totally unreadable and ununderstandable for
most people working in Asian countries.
A clearly fraudulent inscription: this loupe contains a single
glass cylinder (dismantled, right), instead of the indicated
"five elements" of the 20x loupe edge.
Two lenses at the edges (separate 10x and 20x, "butterfly" design), length 52 mm, in plastic container.
Now, as you might be pre-loadad with anti-Ebay prejudice,
please have a look at the almost identical misspelling on the loupe shown below,
Just guess, how many lenses are in there? One?
Left: Highly corrected (anastigmatic), chrome-finished 20x loupe with five
optical elements. As to be expected for a loupe with high magnification it
has a low lens diameter and is exceptionally small.
Of course, what counts in the end is not so much the technical
type of the optical system but the actually visible performance. Good testing objects
are crisp black inscriptions on white paper. The best loupes will provide
images which are perfectly well defined throughout the whole field of view and which
show no signs of colour fringing at all (yellow edges, in very poor products
even several edge zones of various colours).
10x loupe "Liberty #42.02", from Ebay, with beautiful finish. Lens diameter 18 mm. Came in an onion type packaging, in nice printed cardboard box, labelled as "EXPORT QUALITY", therein fine LIBERTY-packaging paper, with gold colour seal print "Made in India" und a nice black housing. This is one of the loupes which we didn't dare to dismantle in order to look for potential triplet disappointments. It is definitely very nice already as-it-is.
One more typical Internet offer: the "ZIESS GOLD, GERMANY, 15 x, SERIES M" comes via Air Mail from Thailand (Honni soit qui mal y pense). In any case at least the etui is not a Zeiss company copy.
In case of doubt the lenses of a loupe should have no noticeable
Some salesmen of loupes do use poorly defined or empty, overdone terms in order
to characterise their products. You will find "optical glass", "silicatic glass",
" ground glass" and many other word vapour specifications.
© Text, images and video clips by
Martin Mach (firstname.lastname@example.org).