The World of Microscopes: Straight & Compound styles

The World of Microscopes: Straight & Compound styles
What’s a Demodex?  It is a tiny mite, far too small to be seen with the naked eye.  It is usually completely harmless and lives on your hair follicles, such as eyelashes.  Nearly 98% of all humans have two different kinds that enjoy our company, Demodex folliculorum, and Demodex brevis.  They have 48,000 relatives that don’t like us (sort of like Thanksgiving dinner).


If they go wild because you go weeks without a shower, and studiously avoid water or any basic sanitation, then sure, they can exacerbate conditions like hair loss, skin rosacea, and dry skin scaling.  Crusty stuff on your eyelashes is usually a sign that you might want to pay more attention, and maybe clean your eyelids with no-tears baby shampoo and a Q-tip once in a while.

However, since they're harmless and nearly impossible to get rid of, it's probably best to think of them as best-friends-forever that always keep you company.  You’re never truly alone!


          We know things like this because, possibly as early as 1590 C.E., Hans Martens and Zacharias Janssen built the first microscope.  There are no patent documents, and the claim was made 65 years later, in 1655, but several scientific historians accept this as the origin.

 Strictly speaking, however, the simplest microscope is the handheld magnifying glass.  This was already known, having been “invented," or at least "first-described" in the mid-1200s (date uncertain) by Roger Bacon (1220-1292).  He delineated the principles of magnification, so he has a pretty good claim.

Magnifying glasses were in use much earlier by the Greeks and Romans, as blobs of glass that could be used to focus the Sun’s light and start tinder burning for a campfire.  Some wealthy Romans were known to look through polished gems to help them see actors on a distant stage!

In fact, as a military man and Natural Philosopher (doctor), Pliny the Elder, who lived from 23 to 79 C.E., was noted for using a glass bulb filled with water to focus sunlight to cauterize wounds.  Ouch!  Yes, it would kill germs and stop bleeding, but it was certainly slower and hurt almost as badly as the other cauterization and sterilization process of using a red hot poker from a fire.  Handy, if you didn’t happen to have a fire already burning…

Compound Microscopes

What Martens & Janssen built in 1590 was called a compound microscope because they used two lenses.  Both were biconvex, meaning they possessed round surfaces on both sides like two spoons held front-to-front.  There are several different ways to grind lenses, such as with concave curves on both sides, concave on one and convex on the other, or with one side completely flat (planar) with either shape on the opposite side.

How do Microscopes Magnify?

As to the actual mechanics of it, a lens changes the angle of the light passing through it.  The eye sees that angle and interprets it as a change in size.  By filling the whole field of view with just a portion of what would be seen without the lens, it, therefore, appears much bigger than reality.

How much do they magnify?

Let’s say that an objective lens (the one closest to the “object” being viewed) enlarges its subject four times (4x), and the ocular (eyepiece) lens enlarges 10x.  To find the total magnification, you multiply the first number with the second number. In this case, that would be 10 × 4, which would equal 40x

A 10x eyepiece with a 100x lens would magnify 1000 times.  The practical maximum magnification with a light-based microscope is 1500x with the theoretical ability to see down to 200 nanometers (nm) because that is half the wavelength of violet light, the shortest wavelength color we can see the visible spectrum.  Anything else would be too small to resolve.

          This means that we can see things as small as bacteria, but we cannot see viruses.  Neither can we see DNA, which is even smaller than a virus or, most notably, atoms.  For that, we need a far more sophisticated microscope that paints a picture with electrons, which are smaller than the wavelength of light.  We’ll talk about those in an upcoming article.

Usually, with light-based microscopes, there is a downward pointing turret that holds between three and five lenses.  Typically they will be 4x, 10x, 40x, and 100x, sometimes with an additional lens that can be used with a drop of oil to exclude any air in the gap to provide a better image.  Though seldom required, lenses can be unscrewed and replaced with different lenses, depending on needs.


Elderly Microscopes

          So what are these “straight microscopes” that I’ve heard of?  They’re still found in some schools, and even Colleges or Universities.  Why do people hate them? 

For an answer to that question, you might want to talk to the Occupational Safety and Health Administration (OSHA) about that.  They were a genuine pain-in-the-neck!  As invented, microscopes were entirely vertical because investigators often looked at uncontained liquids.  Since then, we've developed ultra-thin glass sheets that keep our samples in place, even if tipped.  

          Yet the design persisted, even after that, and researchers frequently ended up with permanent injuries from standing directly above a microscope with their neck bent to a ridiculous angle.  Obliged to be still for hour after hour in order to count the number of cells in a sample—and being unable to look away because you would "lose your spot"—took a heavy toll.

          Nowadays, we have introduced mirrors and prisms to alter the light path so the sample can remain horizontal if needed.  Newer devices provide eyepieces set at a comfortable viewing angle; some are adjustable from only slightly tilted to horizontal.  Now the only remaining serious problems are eyestrain or mental exhaustion, but at least we’ve eliminated debilitating physical injury as a job requirement.

Modern Microscopes

          The older microscope above had only one magnification because it lacked the multi-lensed turret found on more modern scopes.  You may have also noticed that it has a mirror beneath the sample.  Microscopes use “under-lighting” to illuminate samples; since they had no electric lights back then, it was either reflected daylight or candlelight when they wanted to study something.

          Slightly more modern scopes were provided with a hinge joint (red circle), so the scope could be tipped towards the user to ease neck-strain.  And, while still equipped with a mirror, it also had a battery-powered light that came on when the mirror was reversed into a downward-facing direction, with either a mercury-switch or an actual physical, electrical connection.

Still, the design was flawed because the stage for holding the sample (green) was on the opposite side of the vertical support column.  To insert a sample slide, you had to let go with one hand to bring it around the upright and then secure it to the stage with spring clamps while looking around the column.  Just bad design!

          Modern scopes have the upright in the rear, allowing direct and easy access to the stage.  Also, instead of one crude focus knob (blue) like the older scopes, modern scopes are equipped with a dual knob (purple) where the outer ring does the gross focusing, and the inner knob does the fine focusing.  This makes it much easier to achieve good results. 

The light source has been improved, too.  Rather than a mirror or light bulb with irregular patchy light, the design incorporates a diffuser to provide a featureless and even field against which to examine our samples.

Even the stage has been improved.  Instead of physically moving the sample, which at high magnification is very inaccurate, now the stage itself can be moved back and forth and left or right, with extremely precise rotary controls.  We’ve never had it so good!

The Takeaway

          Light-based microscopes continue to evolve.  In our next installments, we'll have a look at sorts of worthy improvements in the world of microscopy.   Whether we’re using dyes, stains, or polarised light, there much more to be seen in the realm of the very small!

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