USB microscopes (I)
A Google search with the term "USB microscope" will return several hundred thousands
of respective web pages and commercial offers within fractions of a second.
We are going to present one of those miraculous instruments which will arrive
by mail after a rather modest payment of, let's say 20 US$.
No name USB microscope (Ebay), with inbuilt
LED light source, a simple stand and a transparent ruler for length calibration purposes.
The LED light power can be adjusted by means of a turning knob (bottom right).
We had been thrilled by those numerous thoroughly
positive comments on USB microscopes which can be found all over the web, though
mostly aired by people who appear to have no previous expertise as microscopists.
Moreover, there is always some kind of goodie measurement software included - with an
impressive list of features. On the other hand those USB instruments definitely
don't look like solid, metal geared classical microscopes. In fact a quick glance into the
objective "face" reveals a tiny black hole - obviously not identical
with the front lenses of some of those old fashioned, expensive microscope objectives.
USB microscope (Ebay), front view revealing
eight illumination LEDs and the front lens opening. The lens itself is somewhat
recessed and therefore not visible on the image.
Two push buttons are serving as a camera shutter
and a digital zoom power selection respectively. Similar to digicams you should
forget about the digital zoom, it is just a gadget. Furthermore there is a big
milled wheel working in a rather sophisticated manner as a combined magnification (25x/200x)
and focus tool. In the position on the left you will be focusing in 25x mode,
in the position to the right in 200x mode.
All the other functions will be available via computer,
with an acceptable software, various preview modes, video and still image capture, scale overlay etc.
The calibration ruler has a millimeter division. No, your eyes
are not fooling you now, you are actually reading "millimeters" here and not "microns",
the typical microscopical unit. Nevertheless this scale will still serve perfectly well in order to provide you
with a feeling for the magnification and image width of the instrument. Just have a look at the two following images:
USB microscope in milled wheel position "25x".
Image width ca. 4 mm.
USB microscope in milled wheel position "200x". Image width roughly 0.5 mm.
Internet microscope advertisements have a sad tendency to
present their demo images in a tiny postal stamp size. In case you should suspect
that this tiny image format might be perfectly suitable to hide the weaknesses
of the respective instruments: well, you might be right.
In order to provide you with a more appropriate, better impression of the image
quality we have been using a European 10 EUR bill as a microscopical test object.
The first following image is showing the respective USB microscope imaging result,
the second one the same situation as seen with the classical Russian
MBS-10 stereo microscope :
10 € bill, detail, as photographed by means of the USB microscope, magnification reading "25x".
Image width ca. 3.5 mm.
10 € bill detail, as photographed by means of the mit MBS-10 stereo microscope.
Image width ca. 1.5 mm.
So, at first glance the USB microscope appears to be quite close to the more expensive stereo microscope.
And agreed, both instruments are definitively better than nothing (your unaided eye). But the big difference is
that the field of view of the classical stereo microscope is much bigger, providing a fantastic overview, 12 mm in width:
10 € bill, detail, as photographed by means of the MBS-10 stereo microscope.
Image width 12 mm. The small green frame is the marking the detail which was used for the comparison above.
So let's resume: The USB microscope might in fact serve
as a definitely-more-than-nothing tiny helper. But the classical MBS-10 microscope
is providing about the 50fold (!) visual object area at the same magnification, thus
being much more valuable in order to gain a wide object overview. All in all we think
that the USB microscope has to work hard in order to compete with a (low mag) stereo microscope
and that it will never be able to replace a (higher mag) classical compound microscope,
neither in terms of usability nor resolution.
And how about the tardigrades? You will see, in the next issue.
© Text, images and video clips by
Martin Mach (firstname.lastname@example.org).
Water Bear web base is a licensed and revised version of
the German language monthly magazine
Style and grammar amendments by native speakers are warmly welcomed.