The Loupe, Microscopes and the SEM

Getting to the heart of the matter in more ways than one

A collection of thoughts

By Paul James.

So you are peering down the eyepiece of your
compound microscope and settling in to some interesting views of your favourite subject. It is winter, and the light that radiates from the illuminated field probably appeals in more than one way. For a start it is comfortably bright, which subconsciously imparts a sense of warmth, and whatever we have chosen to scrutinise also has a fascinating attraction too. A static specimen mounted under a coverslip can be rewarding and of course can always be referred to at anytime. The living specimen is however different in many ways not least of which is that it is a one off event which creates a feeling of theatre : a situation you might not see too often if indeed ever again. Aside all the peripheral technical necessities which are required to be in place before we are able to view our quarry, the perusal of the subject is at the heart of the observation.

The broad range of subject matter is almost endless of course and each portion will draw a variety of observers who are keen in their fields. Many others might be more diverse in their interests which I think is common amongst amateurs of whom a fair proportion will also take a deep interest in the mechanics and optical functions of the microscope.

So we are irrevocably curious it seems, which presumably must persist in other matters concerning microscopy ? Can curiosity be fueling also our desire to improve the quality of imaging in order to reveal more information about the subject ? I think this is probably true and compares to the instinctive desire to clean a window so it makes observation of the view more clearly rendered. We have this innate urge to clarify the subject of our attention in the clearest possible way in order to make an assessment, whatever that might be. The vast majority of microscopists if given the chance wound happily opt for improved imaging if it were to render the subject more clearly. A rather obvious premise you might feel, but though the observer would feel even more engaged with a crisper more realistic image it is ultimately limited by the nature of light and the physical limitation too of the optics in use.

Nevertheless the imposition of these restrictions , as well as manufacturing limitations still allow us to scrutinise objects with a wealth of detail from the compound microscope. Subconsciously there will always be a desire to get closer to the subject, but we must eventually arrive at a point in all this which serves little to further understanding of the biological processes ? In fact I'd say that the vast majority of the visual changes throughout microscopic life can be witnessed within the limitations of optical microscopy as it stands today.

Quite some time ago the SEM ( Scanning Electron Microscope ) had been perfected promising even more spectacular imagery of both biological and non biological subjects. Today the resolution limitations of the best SEM's are down to around 2 Angstrom units ( 0.0000000002 metre ) which translated into meaningful terms puts its resolving capability at around a 1000 times greater than that of the x100 oil objective , with an amplification factor of around x 1000,000 to make this visually discernable ! This quite astonishing quantum leap in detail capture compares roughly between the naked eye's resolving limitations and the those of the light microscope !

Even the average SEM can easily resolve down to about 100 Angstrom units and provide an image scaling of about x5 up to around x 50,000 which would cover everything imaginable....... I'd have thought? One of the great virtues of the SEM aside resolution is its huge depth of field potential : a facility severely limited in the light microscope. However, all this comes at a sobering cost both in monetary terms and in the lengthy time of technical manipulation which is complex, and the preparation of the specimen too which also has to endure several minutes of vacuum and high voltage electron bombardment.................some insects survive I'm told ?!

So how does the imaging from the SEM appear in comparison with its lesser cousin the light microscope ? No doubt many of you will have seem many of its images, which are in B&W but possess remarkable detail and depth of field it must be said. Having seen a fair number of these images I can't but wonder why my enthusiasm for this almost limitless quest for detail has waned, especially concerning the inspection of botanical and zoological materials. Seeing almost robotic images of insects and plasticised cellular renderings of stems and leaf surfaces etc., raised more questions than answers. True, the near molecular world appears dust free and reliably regular in form, but for me there seems to be something missing from these images, and frankly I cannot understand why, despite the limitations of B&W imagery. Perhaps to initial 'wow' factor is followed by an anticlimax in the ensuing revisits to these images because we simple can't process them into believable entities in our minds ?

Of course the SEM's imagery is an artifice of sorts relying on the interpretation of electron reflection off the subject's surfaces, which is converted into light via a CRT screen which then has to be imaged with a camera. This convoluted process cannot be expected to provide easily digestible photographs which our viewing psychology readily absorbs as being run of the mill day to day imaging. Without doubt detail is there in abundance but unless this is of prime importance the value of these images do not seem to justify its expense and efforts in sophisticated manipulation as well as the careful mounting and preparation of the subject matter, which often include gold plating.

Any potential desire I have had to own and use an SEM has been deflated by these pragmatic notions, such that it would in my view be futile and pointless to contemplate such ownership. The SEM is undoubtably a marvel of electronic and mechanical engineering and had I a deep interest in material sciences then maybe I'd reconsider its use.

Rather than seeing all this from a negative perspective, I have with good reason toyed with the fact that light microscopy has all the essential capabilities of satisfying my interests in the almost limitless world of microorganisms, which I'd imagine many readers can identify with too.

At the completely opposite end of the observational spectrum comes the humble, centuries old magnifying glass ( the loupe, eyeglass, magnifier etc.. ). It has to be the simplest optical device in current usage and with very good reason of course. They usually range from around x 3 to x 15 either in single element or multiple glass and also achromatic/aplanatic forms etc.. its great virtue is that it needs no instructions for its use and must rank as the most common of all magnifying contraptions on this planet ! Even those who consider themselves not having any interest in microscopy must have peeped through a loupe of one form or another with consummate ease without even thinking about it ?? Of course the image that we see with it is a simple extension of what we put in front of it but on a slightly amplified scale, so no questions of what is being looked at need arise. However, because of its low ranking in the vast range of optical aids it might be considered to be almost a minor adjunct to microscopy, whereas 'in the field' practitioners often find it of great value being able to whisk it out of the pocket in a few seconds yielding the user a rapid and close up view of their chosen quarry. A really well designed and crafted loupe with good coatings can sport a very impressive image indeed leaving the observer in no doubt about the intricate beauty of the natural world. Initial concerns about the cost of a quality aplanatic achromatic forms should be tempered by its durability, reliability, and simplicity of use during a whole lifetime.

In my view and no doubt many others the low power stereo 'scope can provide the most realistic views of macro/micro forms for rather obvious reasons. Using a quality example of this breed of microscope can genuinely bring about a feeling of intimacy with the subject, and as such deserves its undeniable popularity. Its Achilles heel even in the very best models is the restricted depth of field at higher powers which means that the amplification of about x 50 is rarely exceeded. Despite this impediment, which can be of benefit in certain cases when we do require the background to be lost, careful selection of magnification is critical, being about the only skill required for successful use, aside of course illumination. Because of the large working distances involved we can light the specimen with a number of sources should we so wish.

There are fundamentally two ways of raising the stereo image : the simplest being to split the light from one single objective into the binocular head which is the modern trend. The older concept was to utilise two separate imaging objectives to supply the binocular head with the stereo image. Both work well when properly designed, engineered and in collimation, but the older Greenough form does have the merit of having a less distorted field, but usually its amplification range is limited to 2 or 3 levels. Ultimately the quality of any optical instrument's imaging is related as always to the skill of the designer and manufacturer's quality control.

In a nutshell the low power stereo microscope is easy to use and can yield amazingly high quality natural imagery which the vast majority of users can identify with or relate to very easily. Naturally its applications vary greatly from geology, biology, engineering ( electronic & mechanical ), archaeology, philately, medicine etc.. Its potential subject range is only limited by the imagination and provision of being able to be placed below the objective.

Having briefly touched on some aspects of the basic methods of observing things small, we are left with a few odds and ends. One primary consideration is cost, and the other one reflects the personality of the individual. In realistic terms the question of cost and affordability for the amateur is usually simplified by the availability of used instruments of which there are literally hundreds for sale around the globe. Ironically, though the loupe is the simplest optical device that has been mentioned here, it is not necessarily the cheapest for the cost of a new loupe can be well in excess of a used compound microscope or for that matter a low power stereo too. Even an oldish SEM can be sought for a little more, though its reliability and condition might surely be a problem.

So in order of complexity and ease of use it seems that the list should start with the loupe, then the low power stereo microscope, followed by the compound 'scope and finally ending with the SEM. Because of the inherent complexity and technical skills to operate the latter two, it follows that those who are not only curious about things small, but have a mechanical bent, or electronic skills must also derive operational pleasure from their recreation too. Combining several interests within one pastime or recreation is very satisfying.

Whatever reasons we have for ploughing our own path through the microscopical world, the fact is we are all different, yet share one particular pleasure. Whether we are using the loupe, low power stereo, compound 'scope or the SEM the process of satisfying our curiosity in its fullest sense is being realised.

All comments welcome by the author Paul James

Editor's note: Paul is reviewing his internet access as at Jan 25th 2006.
Feedback can be sent via the email link above to the Editor which will be forwarded.

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