Tardigrades, naturalists and the triplet distress (II)
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.
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.
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.
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:
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.
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.
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.
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:
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.
Tech specs of the two 10x magnifiers and additional comments:
© Text, images and video clips by
Martin Mach (firstname.lastname@example.org).