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Tardigrades, naturalists and the triplet distress (II)

It began as a rather vague idea: shouldn't it be possible to demonstrate the actual visual impression as seen through several magnifying glasses in order to compare among them? Just in order to "negotiate" between different opinions and judgements.

As you know we have been talking on one hand about simple cylinder lenses (made of one solid piece of glass) and about true triplet systems on the other (consisting of three separate lenses cemented together in order to form a much more complex optical element). Fig. 1 is showing typical candidates representing both systems:

[ Zylinderlinsenlupe und 6 LED-Triplettlupe ]

Fig. 1: Two internet mega sellers, typical representatives of the category "10fold magnifiers for biologists and naturalists". On the left you will see the cheap "10x21MM" folding magnifier with the respective cylinder lens in front of it. The more expensive "true" triplet magnifier and its lens can be seen on the right side of the image. When looking closer at its optical element it becomes apparent that it is actually made up (cemented) of three lenses, with the central one having a slightly lower diameter.

In case you should be in a hurry you might simply scroll down to fig. 6 in order to see the comparison of the optical performance of the two candidates. For a more elaborate discussion please just continue reading.

The detailed technical specs of the two magnifiers are listed on the bottom of this page. Just let's mention that the minimum optical open cross section of the cylinder lens system has a diameter of 20.5 mm whereas the triplet optical open cross section is much less, namely 16.5 mm. Similar as in practical photography this implies that the triplet system is stepped down a little bit, possibly cutting out potential edge problems.

In this issue we are going to illustrate the general image appeal only. Detail resolution and the influence of illumination will be discussed later. In the end of this sequence of issues we will show some very special, collectible high mag loupes.

For the general image appeal we chose a Leica transparency test slide formerly used to check the image quality of slide projectors:

[ Leica Test-Dia ]

Fig. 2: Leica 35 mm test transparency. Simply scanned by means of a flatbed scanner in order to provide an idea about the test object. The outer frame of the b&w checker pattern is measuring 35 mm x 23 mm. Photographers will know that it is not possible to view the total field of such a slide with a 10 x folding magnifier. For this reason they are typically using 4 x or 6 x systems. The hexagonal area in the center of the test slide has a width of 1.75 cm.

The experimental setup for the intended comparision was much more difficult to achieve than one might think at first glance. Obviously, there are a lot of parameters influencing the documented magnifier visual impression and of course the documentation should show the field of view without any camera vignetting or camera objective induced distortion. Afte some experiments we finally ended up with a SONY SEL 2.8/16 wide angle pancake objective. Funny enough, this objective is able to grasp an even wider field of view than the bare eye in close contact with the magnifier. The following image pair is showing the results obtained by means of the simple cylinder lens magnifier (fig. 3a) and the triplet magnifier (fig. 3b) respectively. The red circle is marking the maximum field of view when looking through the magnifiers.

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Fig. 3a: Image taken through the "10x21MM" simple cylinder lens folding magnifier. Please note that the field of view is rather large, measuring impressive 2.5 cm - as a consequence edge effects become visible rather drastically. Incident light, image taken on a small lightbox.

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Fig 3b: Image taken trough the true triplet-"LED LOUPE". Please note that the field of view is much smaller than in the case of the simple loupe, just measuring modest 2 cm in diameter. As a consequence far edge image problems are cut off by the metal fitting, thus providing a more favourable overall image quality impression.

Summing up we can state that the cheap lens and the triplet are both able to provide a thorougly usable image. Furthermore the cheap lens image quality impression might be misleading due to its large field of view. A casual observer looking through the cheap magnifer might judge it as giving a poor image quality - but the most deterring effects are caused by its wider field of view. In contrast the visual impressions ot the triplet system will be considered as close to flawless from edge to edge. But one shouldn't forget that this favourable outcome is partially being caused by the smaller field of view.

When looking at the very center of both comparison images the image quality difference between cheap and more expensive appears to be negligeable. Only when regarding closer, when comparing directly or when looking at high-contrast b&w objects some difference will be noticeable:

[ Leica Test-Dia ]

Fig. 4a: Image taken through the "10x21MM" simple cylinder lens, detail view, concentrating on the center of the field of view. Some color fringes and a slightly greenish tint became apparent, the latter being caused by the slightly greenish glass color of the cylinder lens. Image width ca. 2 cm.

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Abb. 4b: Image taken through the true triplet-"LED LOUPE", detail view, concentrating on the center of the field of view. Image width ca. 2 cm.

Nevertheless we do not want to disappoint those among you who spent more money for a triplet system. When looking at the far edges the difference in quality will become apparent - finally! On the other hand we must admit that the triplet advantage will pay off only modestly outside in the field.

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Fig. 5a: Image taken through the "10x21MM" simple cylinder lens, detail view of the right side bottom edge. But please keep in mind that this area is only of theoretical interest: the wide angle camera is able to document it but it is situated already beyond the aperture of the bare eye.

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Fig. 5b: Image taken through the true triplet "LED LOUPE", detail view of the right side bottom edge. But please keep in mind that this area is only of theoretical interest: the wide angle camera is able to document it but it is situated already beyond the aperture of the bare eye.

Finally and more seriously the direct comparison might help for a practically usable resume, as it is based on a more realistic image center impression:

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Fig 6: The center area of the two magnifers in direct comparions (compiled of partials of figures 4a und 4b, one of them mirrored for better understanding). It becomes apparent that the borderlines of the hexagon look more cleanly when studied by means of the triplet system. Besides, the distance of the inner b&w lines is measuring approximately 0.1 mm - one third of a typical tardigrade body length.

Now it is up to you decide what might fit your needs. In any case we would like to suggest that you should not buy the cylinder lens magnifier from a "professional" dealer for 20 $ and that you should not pay as much as 50 $ or 80 $ for the triplet but order directly from overseas yourself instead.

In case you should plan to spend much more money we recommend to buy magnifiers that were actually produced in your country instead of luxury-feeding importers from China. This is not penny counting but a simple precaution that you will not be regarded as a fool who can easily be ripped off by anybody.

Our next issue will focus on the question how much detail actually can be seen when using those 10x magnifiers. We were honestly surprised when checking this out!

Tech specs of the two 10x magnifiers and additional comments:

(1) "10x21MM" 10fold magnifier (as shown in fig. 1, left side)
When folded measuring 37 mm x 25 mm x 19 mm. Unfolded measuring 62 mm in length. Weight of the one shown: 33.3 g. Lens diameter 20.5 mm, lens height 13 mm, noticeably greenish glass. Actual magnification very close to the triplet lens (ca. 10x). Solid metal housing, probably made of an aluminium alloy. The lens is reversibly fixed within its housing by means of a threaded metal ring. The tool traces are indicating worn out, heavily used machinery. Philips screws with some flight tendency. Sharp edges, poor finish, inscription not very durable. Though appearing rather elementary, this magnifier is well suited for field work, astonishingly well. It can be directly ordered from China for a few dollars. Be warned that local dealers of your contry might declare them as true triplets as well, charging 15 $ for those instruments, telling you after reclamation that they didn't care how those magnifiers were actually exactly made in China!

(2) 10fold magnifier, cemented triplet (Ebay: "6 LED loupe" (fig. 1, right side) When folded measuring 48 mm x 27 mm x 24 . Unfolded measuring 84 mm in length. Weight 50.8 g. Lens diameter 20.5 mm, cut down to 16.5 mm diameter due to the front-end LED illumination ring. Lens height 19 mm. Actual magnification very similar to the cylinder lens loupe (ca. 10 x). Illumination by a ring of 6 evenly spaced sub miniature LEDs the light of which is softed by a resin ring, resulting in an almost shadow free illumination. On/off switch. Electricity provided by three AG7 silver batteries. Ground and top plate made of steel, cleanly cut lens housing, finished in black, probably made of an aluminium alloy. Well fixed bolt (no screws). Soft edges, inscription not very durable. Due to the amount of metal possibly providing a cold feeling when used outdoors. Comes with cardboard box and leather case.
This is a so-called "Steinheil" cemented three lens construction with an excellent optical image quality and it is - as we see it - unrivalled when being used in combination with the 6 LED ring. Good value for money.
International Ebay is offering this magnifier for as cheap as ca. 20 or 25 $ including shipping.

© 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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