USB microscopes (II)

In the previous issue we had presented a typical USB microsope, priced at about 20 USD. The software installation worked flawlessly. After this step everybody should be able to dive deeply into the world of microscopy - at least according to some internet advertisements. We have made a quick test, just sneaking onto the surface of a black leather purse. Point and shoot:

Demo image made by means of a no-name USB microscope (Ebay) showing a detail of the surface area of a black leather purse. The automatic contrast function of the software is generating a graphically interesting structure from the black leather - but the imaging result doesn't really resemble black leather. Magnification setting 25x, image width ca. 4 mm.

Overall it is a mixed bag. The structure appears to be quite okay though there is definitely a slight lack of detail. In the end the microscope software is generating some kind of result which reveals the pore structure of the leather but at the same time fails to properly document color and contrast of the tricky black leather.

Clever microscope dealers tend to boast with "microscopic" images of RS232 computer plugs and other electronic components, all of which will show up with a tremendous depth of field. But, of course, from a true microscopist's point of view most of those demos are merely macro video, loupe mode, not quite microscopic. And you should generally distrust any microscope announcement or advertisement accompanied by stamp-sized demo images only.

Our own "micro" demo photograph of a computer chip (a so-called Eprom), made by means of the no-name USB microscope. Magnification setting 25x. Image width ca. 4 mm.

Also this image is quite okay at first sight, and besides it can serve as one more testimony of the pronounced human genius behind those computer chips. In case of those geometric structures our brain makes up for any imaging deficiencies as we do know that a rectangular area should look actually rectangular, a line will appear perfectly straight etc. But, when looking closer at the surrounding articifical resin or ceramic surface areas of the chip (see image below) you will notice severe compression and contrast artifacts which are a typical feature of USB microscopes as well. So, they might serve as a perfect tool for repair work or technical production control but they might be not as good when true representation of microscopic detail has to be performed:

One more demo photograph, made by means of the USB microscope. Same object, but with focus on different object properties. The top and left image areas suffer from typical compression artefacts. Magnification setting 25x. Image width ca. 4 mm.

Tardigrades have no technical, rectangular structures, which might be self-explaining to the human brain. The following photomicrograph, made by means of the USB microscope shows a tardigrade in its dry form (a so-called tun) at the maximum magnification of the instrument. Whereas the chip structures above might look fair or acceptable at fist glance, we get some kind of watercolor effect in this situation:

Demo image, made by means of the no-name USB microscope. Tardigrade "tun" (i.e. tardigrade in the desiccated state). Magnification setting "200x". Image width ca. 1 mm.

For comparison we are showing the same situation as photographed under a low magnification MBS-10 stereo microscope (a so-called dissecting microscope). Obviously the stereo microscope does a slightly better job than the USB microscope. Its image does in fact look more realistic. But of course both instruments are far better than the naked eye. Without a magnification device the tardigrade "tun" is far below the visual detection limit. As an aside we have to note the USB microscope is boasting with a "200x" magnification setting. But the actual image appeal and level of detail might be better characterized as a typical "30x".

For comparison: the some object as seen under a classical stereo microscope (MBS-10 dissecting microscope). Similar level of detail but more realistic appeal. Image width ca. 1 mm.

Concluding we might argue that those two instruments were not too far apart. With respect to detail resolution this is perfectly true. But we should not forget that the true resolution of "200x" is far below the "200x" resolution of a classical compound microscope - you see, we have just been comparing with a low-mag dissecting microscope. And moreover, the main difference is in usability. The positioning and focusing of the USB microscope is quite cumbersome, in particular at higher magnifications. And even worse, the field of view is very, very narrow, so tiny objects might be difficult to find and difficult to keep in focus. On the positive side the USB microscopes is offering inbuilt still image and video. Furthermore it has sophisticated measurement capabilities.

Still shot showing the "CoolingTech" software at work. Lots of possibilities, e.g. length, area and angle measurement. When keeping in mind the low price of the instrument and that the software is just a free add-on, bundled with the microscope the value for money relation appears quite good.

In a nutshell, we do not want to condemn the cheap USB microscope. It certainly has some advantages. The software is fun and the instrument is definitely better than nothing, far superior to unaided human vision (and even better when compared to typical senile vision capabilities!). Nevertheless we have to conclude that this instrument might perform satisfactorily when used for technical inspection work - but it will not be of great practical use for any tardigrade investigation as you will spend much more time on positioning and focusing than on the actual tardigrade investigation.

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
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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