CAT | Education
In today’s modern era, it’s almost impossible to imagine a time when we didn’t know about microscopic particles and structures; magnification is a fundamental part of everyday life, from a pair of reading glasses to the side mirrors on a car. With the birth of the optical microscope in the 17th century, scientists were able to meticulously document, research, and discover a world of things normally invisible to the naked eye. It seemed as though the wonders of the microscopic was infinite – until the 1930s, when it became clear that optical microscopy wasn’t telling the entire story. There were forces at work that were far too small for even the most powerful lenses to see; at some point, the image simply couldn’t resolve clearly. It seemed as though optical microscopes had been pushed to their furthest possible limits. But how could something be too small for light to see, and how could you possibly examine it?
This set of problems was the catalyst for scientists to begin branching out from light-based microscopy. The theoretical framework explaining the limits of light-based magnification were already in place. The issue lay in understanding how light worked, and why it failed at certain magnifications. Visible light is electromagnetic radiation, part of a wide spectrum of rays that stretches from radio waves to X-rays, microwaves, gamma rays, and more. All EM Radiation is made of particles called photons, which travel in a wavelength; the speed and frequency of that wave will determine what sort of radiation it is, and how it interacts with various objects. X-rays, for instance, have a wavelength that is too short to bounce off of human flesh, but does reflect dense material like bone, allowing the doctor to clearly see your broken wrist. UV radiation can penetrate the skin enough to cause a sunburn, but we can’t see the rays with our eyes.
We are able to see objects because visible light bounces off of them and returns to our eyes. When that wavelength encounters an object, like a sample on a slide or the magnifying lenses of a microscope, the interference will cause the wave to spread out and weaken. As the light passes through a smaller and smaller space, it will scatter more and more. This phenomenon is called diffraction, and it is the major limit of optical microscopy: at a certain point, the photons are just too big and clunky to accurately bounce off of the sample and resolve clearly.
All of this was proven in 1873, when physicists Hermann von Helmholtz and Ernst Abbe demonstrated that optical resolution was dependent on the wavelength of the light source. They posed the crucial question: what if you could somehow use an illumination source that had a smaller wavelength than light? It was purely theoretical; the existence of electrons wasn’t proven until 1896. But the idea stayed around in various scientific circles; the theory that electrons could travel in a wave was proposed in a 1924 paper, and in 1926 German scientist Hans Busch showed that magnets could be used to direct a stream of electrons in a specific direction. The problems were in place and the theories were quickly being proven: it wouldn’t be long before scientists broke through the limits of light and found a way to see the invisible all over again.
We are often asked about immersion oil so here is a basic primer. Immersion oil is used with high power objectives, typically 90x or 100x.
Light microscopes have an upper limit to their resolving power of marginally over 1,000x. At this level of magnification, the microscope needs to direct every available amount of light in order to achieve a clear image. Since light is refracted and scattered in the air between the objective lens and the slide cover, immersion oil is used to capture much of that ‘lost light’.
In summary, light refracts through air and glass at different angles. The refractive index of air is 1.0 and that of glass, 1.5 so there is considerable refraction between the two. The immersion oil helps to reduce the refraction since it has a refractive index equal to glass. As a result, it forms a continuum between the objective lens and the slide, thereby successfully ensuring that more light is directed towards the specimen and ultimately, a clearer image.
Oil immersion objective lenses are typically engraved with the word “oil”, “immersion” or “HI” (homogenous immersion). They are manufactured with sealants to prevent damage from the oil.
Immersion oils are commonly available in two viscosities-low viscosity (Type A), and high viscosity (Type B). They are often labeled with a refractive index of 1.515. The low viscosity oil is applied to the airspace between slide and objective, the high viscosity oil is applied between the condenser and the slide.
How to Use it: Type A – Low Viscosity Oil
The majority of applications require Type A oil, which can be used as follows:
- Locate a specimen on the slide and center it in the image field.
- Rotate the nosepiece until the 100x objective lens is just to one side of the slide. Place a single drop of immersion oil on the slide cover slip and place a drop directly on the objective lens. Combined, both drops ensure no air is trapped in between.
- Rotate the 100x objective into place and adjust the fine focus to fully resolve the image.
It is very important to carefully clean the oil off your objective lens before it dries.
- Carefully wipe oil from all glass surfaces with a folded piece of clean lens paper.
- Moisten a piece of lens cleaning paper with lens cleaning fluid and wipe away any residual streaks of oil.
Any day now, an invasion will begin. Unsuspecting people up and down the Eastern seaboard from New England to North Carolina will run for cover. Weddings will be interrupted. The news channels will work themselves into a frenzy – and your lawns, trees and gardens will buzz with bulging, red-eyed invaders. Martians? No. Simply, the hatching of billions of Magicicadas.
For the past 17 years, billions of the inch-long bugs, which entomologists ominously refer to as “Brood II”, have been lying dormant underfoot. Quietly munching away on tree roots and vegetation 2-3 feet below us, they have awaited Mother Nature’s call to complete their 17 year life cycle.
That call happens when the soil temperature in their underground home climbs above 64 degrees Fahrenheit. Over the course of the next few weeks, billions of them will emerge and swarm with the primeval goal of mating before they die. Despite their ghoulish looks, they actually are quite harmless to humans and animals. For the most part, they hang out in trees and shrubs for a few weeks and then die, at which time their offspring venture underground to begin another 17-year cycle.
Even though this year’s brood is forecast to number in the billions, most of us won’t even see them. We most definitely will hear them. The male Cicada makes music by pushing air through vibrating organs in their abdomen, and quite effectively at that. As they sing their mating cry, a tree filled with males can fill the evening with sound volume approaching 90 decibels!
Apart from their rare appearance and song, what exactly are Cicadas good for besides water-cooler commentary? Well for starters, they’re edible! They are eaten by a wide variety of animals…….including humans. While not quite rising to the popularity of chocolate-covered crickets, they still hold their own at the adventurous dinner table. In fact their hearty flavor, which some intrepid souls describe as asparagus-like, can be found in a surprising variety of dishes like cheese, quiche, casseroles and
even dessert, for those ardent aficionados. Apparently, they are best eaten immediately after hatching which typically, occurs at night. Luckily, they are quite torpid after hatching so they can easily be scraped off the tree branches.
Abundant food, totally organic, nutritious, free and hilarious……..it didn’t take long for us here at Microscope.com to decide to hold a contest for the best Cicada recipe.
So dust off your family’s favorite Cicada recipe and send it in. We’d love to hear about it and you could have a chance to win a new microscope. One more reason to enjoy this “Season of the Cicada”…or should that be Cicada Seasoning? Bon Appetite!
Just send us an email, with recipe attached, to [email protected], anytime between now and the June 15, for your chance to win a new Omano OM115 compound microscope. The winner will be announced in a followup blog post.
We’re surrounded by an abundance of technology, nowadays so it can sometimes be hard to imagine what it was like to look through a microscope for the very first time in the 1600s. Before the invention of the compound (multi-lensed) microscope, people believed that the world was comprised solely of what could be seen with the naked eye; it must have been overwhelming to realize what humanity had been missing! Once optical microscopy took off, scientists could finally get a detailed look at everything from well-known insects to completely new bacteria and understand how the tiny structures of a material affected its behavior.
Scientists are well-known for conducting experiments and documenting every detail of their actions. So it’s not surprising that the great analytical minds of the day began to sketch out the details of what they saw under the microscope in order to preserve the images for future reference. These images came to be known as micrographs, and they have evolved alongside the microscope in terms of their level of detail and use of technology.
Initially, micrographs were hand-drawn sketches detailing what the observer saw on the slide. One of the first known images made with a microscope was drawn by Francesco Stelluti, who published a sheet of bee anatomy in 1630. Thirty-five years later, scientist Robert Hooke wrote and published Micrographia, the first major book about microscopy. The tome detailed his observations: the eyeball of a fly, a plant cell, insect wings, and a huge fold-out engraving of a louse. Micrographia was a monumental best-seller that also coined the biological term ‘cell’ after Hooke’s famous inspection of a piece of cork.
Basic sketches remained an easy method for documenting microscopic images for many years. When photography technology caught up, people would often simply hold a standard camera up to a microscope eyepiece and take a picture; after all, the camera was designed to resemble the viewpoint of a human eye, so it made sense to try to capture the slide permanently by exposing it to film. This technique is called the afocal method’. A typical optical microscope emits parallel light rays from its source up into the ocular, so an image can be created using a camera that is made for capturing very distant objects; those lenses are designed to work with parallel light as well. The eyepieces of both the ocular and the camera must be carefully chosen to work together to capture a clear image.
The direct imaging method is far more straightforward: both the eyepiece of the microscope and the lens of the camera are removed, and the camera is placed on the microscope tube so that its shutter surface matches the primary image plane projected by the microscope. You can also purchase mechanical adapters, which attach the camera to the microscope tube directly and allow for a much clearer method of focusing. Digital photography has made micrographs much easier to produce. Modern microscopes may contain a built-in camera and USB connection, which will allow you to plug them into a computer and record images directly onto the hard drive. However, a more flexible approach is to buy a standard microscope and add an external microscope camera. That way, you can use different cameras on the same microscope and vice versa. As important, you do not need to buy an entirely new unit if the camera software fails. Whatever your method, microscope imaging, or photomicrography, has grown and changed alongside microscopy, recording humanity’s findings for future research and posterity.
A microscope can change a student’s life forever and introduce your child to the smallest wonders of the world around him or her. But microscopes aren’t toys; even the simplest student-oriented device contains some very delicate parts. It’s important to learn how to handle and care for your new microscope properly, so that you can enjoy your device for years to come. Here are a few basic do’s and don’ts for two of the most important parts of a microscope: the illumination source and the lenses.
Light microscopes need a light source to illuminate the sample you are viewing. Modern microscopes typically employ tungsten, halogen or LED light bulbs. Field microscopes can employ ambient light although the first rule is never to use your microscope outside in direct sunlight as it can damage your eyes. Halogen microscope bulbs can become very hot to the touch. If you need to replace the light source, turn off the microscope first and unplug it; this will allow the bulb to cool and prevent possible electric shock. Always use the correct light bulb; different brands require different bulbs that are calibrated to work with the lenses, so trying to swap out one type for another may cause damage to the microscope. Use your microscope in a well-lit room, and always place it on a flat surface.
The lens of a microscope is the engine of the microscope. without it, your magnification efforts are futile. Compound microscopes have two types of lenses: the eyepiece, or ocular, which is what you look through; and the objective lenses, which are the primary magnifiers and are typically positioned directly above the stage on which the specimen will sit. Most compound microscopes include between three and five objective lenses that are mounted on a rotating turret. Magnification is achieved by multiplying the value of the eyepiece by that of the objective lens. For example, a 10x eyepiece and a 100x objective lens creates 1,000x magnification.
All microscope lenses are delicate and should never be touched with bare hands. If the lenses have dust or oil on them, clean with special lint free, lens tissue and a microfiber soft cloth. Neither of these will scratch the glass the way normal tissue paper would. Lenses can be damaged through improper cleaning techniques so it is important to use correct materials and if necessary. Begin by blowing away any dust using compressed dry air; there are some high-grade canned air products made specifically for optical equipment. Moisten the lens tissue with a solvent-free lens cleaning fluid and never dry wipe the glass.
Some microscopes use immersion oil, which reduces the amount of light refraction and provides a clearer image of the sample. This technique is achieved by immersing both the objective lens and the specimen slide in the oil. Always make sure to clean all of the oil from the slide and the lens once you are finished; any leftover residue can flow into the microscope casing and damage its components. Follow the instructions for oil immersion, carefully and clean all areas that have come into contact with the oil.
False Magnification…. False Advertising or both? Be careful about buying a microscope that advertises 2,000x magnification. 2,000x is double the magnification for which standard light microscopes are designed so 2,000x must be too good to be true – as indeed it is!
Claims of 2,000x are achieved by the simple expedient of adding a set of 20x eyepieces to the standard 10x eyepieces. Magnification is achieved by multiplying the power of the objective lens by the power of the eyepieces. So 20x eyepieces x 100x objective lens = 2,000x total magnification, right?
Well, yes…..and no! Yes, the total magnification of the image increases, but the resolution of the image will degrade to the point where it is useless. This is because those higher power eyepieces push the total magnification above the Maximum Useful Magnification of the microscope. They higher power eyepieces create False or Empty Magnification. This is similar to when you try to zoom in on a slightly blurry pdf on a webpage. The image gets bigger but there is no improvement in resolution.
Maximum useful magnification is approximately equal to the size of the numerical aperture (N.A.) multiplied by 1,000. So, for a microscope with an NA of 1.25, the maximum useful magnification is approximately 1,250x. Anything above this maximum produces false magnification. The additional magnification yields no further useful information or finer resolution of detail. Quite the contrary. You will likely experience severe degradation in resolution. To quote Nikon, “In fact, excessive magnification introduces artifacts, diffraction boundaries and halos into the image that obscure specimen features and complicate the interpretation of visual interpretations”. In other words, the image gets blurry!
That is why all standard light compound microscopes are designed and sold with 10x eyepieces as standard and 100x objective lens as the largest obejective lens. At a 1,000x magnification, you do get higher magnification and improved resolution over, say, 400x, because the total power of magnification does not exceed the maximum useful magnification of the microscope.
Now, with some better quality microscopes you can get away with using 16x eyepieces. 1,600x is not such a stretch from 1,250x when using a microscope with NA 1.25. But 20x or 25x eyepieces? Not only will they not work efficiently but they are likely to frustrate your experience.
Those websites advertising 2000x magnification? False Magnification and false advertising in my opinion.
One of the major intangible benefits of our work here at Microscope.com is the ability to positively impact the lives of school children the world over. One such example comes to us by way of an email recently sent by customer Jeri Bennet, a member of the United Methodist Church. She recently traveled with her husband on a missionary trip to a small rural school in Mukono, Uganga.
Accompanying them was a freshly serviced pair of Omano OM118-M4 student microscopes, designed specifically for introducing young scientists to the fascinating world of microscopy. In a land where basic school supplies are at a premium, these microscopes were received with great enthusiasm by students and teacher alike, as shown in the images below.
Located in the Lukojjo village in Mpoma parish, a sub-county of Nama in the Mukono District of Uganda, HUMBLE School first opened its doors in February 2004, as a day and boarding primary school with initial enrollment of approximately 116 pupils and nine teaching staff.
Under the leadership of United Methodist Bishop Mike B. Watson, over 50 of these children have now graduated from HUMBLE and are enrolled at nearby secondary schools. Microscopes such as these not only help to educate the children, they also play a critical role in the ongoing struggle against Malaria and other infectious diseases and it is our continuing privilege to honor their efforts and the hard work of customers like Jeri Bennet.
I was looking around the Web today for news about microscopes and ran across an interesting lifestyles article in the Daily Pilot out of Newport Beach, Ca. Headlined “Respect for the little things,” this piece by Michael Alexander talks about Science Adventures, a local elementary school’s after-school program that teaches first-graders a little piece of science at a time.
Currently, the children are learning to make microscopes the old-fashioned way, out of lenses and cardboard tubing, to view salt, sugar, even ants … who must appreciate that the kids are not using a magnifying glass on a sunny day!
I was surfing the Web for microscopy news when I ran across this heart-warming story about a woman who donated her deceased husband’s beloved microscope to her hometown high school in Farmer City, Illinois.
Kathy (Schield) Patterson, who now lives in Fairfax, Va., donated the 75-pound Nikon Diaphot to Blue Ridge High School. Her husband, Mike, was a research scientist and college pathology professor who died a few years ago. According to Pentagraph.com, the 1985 model sells for roughly $7,000 on eBay. Science teacher Mike Hendricks says the donated microscope is the best one in the lab. Apparently the slides are pretty valuable, too.