Magnifiers: a closer look (XII)
Professional focal length measurement for amateurs - further results!

In the July issue we had presented the theory behind an advanced focal length measurement method (making up an almost universal micro-optics magnification measurement method!).

The respective practical procedure had been explained in August.

First measurement results had been presented in September.

In September we had already discussed the "10x 6LED" magnifier (fig. 1) and had found out that its actual magnification was slightly below the specified value (9x), a fact that should be considered as a minor sin, if a sin at all. But there was a problem with its big brother (fig. 2), where the imprint is clearly wrong.

Fig. 1: "10x 6LED" folding magnifier - measured magnification 9x. As already explained previously this one has to be regarded as a perfect instrument for finding tardigrades in the dry state - due to its LED light.

Fig. 2: "30x 6LED" folding magnifier - measured magnification 15x.

Technical annotation to fig. 2: At first glance this is looking fine: a combination of a true cemented triplet with LED ring light plus UV plus 30x magnification! Obviously the faulty "30x" specification is a flaw. On the other hand one must admit that the 30x power wouldn't work with a wide housing like the one here - so the user will be better off with the actual value of 15x.
User evaluation: We do greatly prefer the 10x version shown in fig. 1. It appears to provide a better clarity and field usability.

But there are more magnifiers with faulty, erroneous or even fraudulent inscription:

Fig. 3: A hand magnifier made of massive metal - with a measured magnification of 7x (!) which stands in sharp contrast with its "30X36" inscription, signalizing a 30x magnification. Furthermore it is labeled as "MADE IN GERMANY", a statement which shouldn't be taken too seriously.

Technical annotations: The housing is made of massive aluminium with a nice golden finish. The engraving owes its contrast to the grey base metal. The upper part is fixed by means of a precision thread and can be easily removed revealing a comparatively simple system of two big biconvex lenses (diameter 36 mm) which are held apart by a plastics spacer with a height of 13.5 mm.
Our focal length measurement resulted in a 7.1x magnification which is far off from the inscription. Solid metal and glass. Weight 48.3 g.
User evaluation: The housing looks more appealing and definitely less glary than is appears to be on our photograph. You will get a very solid feeling in combination with an acceptable image quality and a rather low magnification. Furthermore it comes at a bargain price.

Fig. 4: A widely marketed, extremely cheap 10x/20x double lens folding magnifier

Technical annotations: It comes as no surprice that this folding magnifier does not contain true triplet optics but simple cylinder lenses instead. The housing is made of solid metal with good quality rivets so there will be no missing screw problems. We measured a magnification value of 7.1x for the "10x" side and 11.1x for the "20x" side. Weight 46.6 g.
User evaluation: Even though the labels a far off from reality this is still a usable magnifier as it has glass lenses and a solid housing. Of course you shouldn't expect an achromatic image. When keeping in mind that the German Octoscop^TM "28x" magnification is in fact only a 20x magnification (see September issue) we shouldn't judge too harshly in this case, in particular with respect to the low price. One simply shouldn't expect true triplets in this product category. Keep cool and think pink!

Fig. 5: A very small "14x Hastings triplet" folding magnifier

Technical annotations: The optics are mounted in a black plastics housing, neatly fitted by means of rivets between the metal plates. The instrument is really tiny, measuring 26 mm when folded. As a consequence you might come along user complaints arguing that those magnifiers were too small to use. But we think that it is better to have a tiny loupe with good image quality than one with oversized lenses and poor image quality. The lens system is a true cemented triplet rendering a flawless image. The measured actual magnification is 12x - not very close to the specification but still acceptable. Weight 10.0 g. We do like the sleek design and the mechanical quality.
With respect to the inscription we should point out the similarity between this bargain "Hastings Triplet // New York" magnifier and those more expensive ones bearing inscriptions like "Hastings Triplet // Bausch & Lomb". Apparently the 14x magnifier shown here is a kind of clone or possibly illegal copy mimicking a Bausch&Lomb product.
User evaluation: This is a small magnifier with slightly stronger magnification than the usual 10x types. The field of view is 13 mm in diameter. Overall this is a quality magnifier, possibly not well suited for universal use but instead for professionals who know where to look at. Those people will not be disappointed as the image quality is very good. Nevertheless the 10x 6LED magnifier as shown in fig. 1 might be more useful for general purposes and for moss sampling - it boasts with the big 6LED advantage.

© 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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