Optical Microscope

Introduction

Since its creation, the microscope has been vital for scientific development. Magnifying lenses had been found much earlier by the Romans upon discovery of glass, probably by mistake. The earliest discoveries were of magnifying glasses that would magnify objects by between six to ten times. It was, however, not till the invention of the compound optical microscope that it was used in life sciences. A compound optical microscope has two elements; a simple central magnifying lens and a secondary lens system comparable to a telescope. For it to work, light is passed through the subject and then focused to the secondary and primary lens system (Petran, Hadravsky, Egger, & Galambos, 1968)

Development of the optical microscope

Around 1590, two spectacle makers from the Netherlands found that a system of lenses produced a much larger image than what was produced by single lenses. They, therefore, made their first microscope, mostly out of novelty (Zenhausern, O’Boyle, & Wickramasinghea, 2001).

The first real microscope was however made by Anton van Leeuwenhoek, who was a scientist and a draper from Denmark. He made more successful microscopes by also working on ways to improve his lenses by grinding and polishing 550 lenses. He made a microscope that magnified an object up to 550 times and one that viewed objects the size of one millionth of a meter. He was the first person to make biological discoveries using a microscope. He saw and described bacteria, yeast, life in water, blood circulation in capillaries. All the discoveries he made were then communicated to the French Academy and to the Royal Society of England in over a hundred letters (Petran, Hadravsky, Egger, & Galambos, 1968).

Hooke’s work was then developed by an English scientist, Robert Hooke and published in1665. He also furthered and advanced studies in microbiology and biological sciences in England. Hooke’s Micrographia was his most famous work. He observed objects under a microscope and drew them himself. He also observed the cells in corks.

The development of microscopes did not progress much for over the next 200 years. In the 1850s, there were advancements in the technology by a German engineer who refined his lenses and made better microscopes. He further employed a glass specialist, Ernst Abbe, to help in the improvement of the manufacturing process of optical instruments. Over time, Abbe studied the principles behind optical instruments which were there before based on trial and error methods (Petran, Hadravsky, Egger, & Galambos, 1968).

With technological advancements, the modern compound optical microscope was discovered. The optical microscope can see an object up to 200nm since is only able to view objects the size of the wavelength of light (Zenhausern, O’Boyle, & Wickramasinghea, 2001).

The optical microscope has since been developed to a digital microscope. In this microscope, an object is no longer viewed on the eyepiece. Instead, sensors the type of those used in digital cameras is used to lift the image of the object. The image is then displayed either on a screen fixed on the microscope or a computer monitor. This advancement has made it easier to use the microscope by making it possible for the user to move their head while using it. Multiple users are also able to use a microscope at the same time (Karrai & Grober, 1995).

Using an optical microscope

The optic microscope serves to increase resolution. It also magnifies an object such that details that cannot be viewed with the human eyes are viewable. Resolution increases the number of observable features while magnification refers to a simple increase in size. The resolution of a human eye is about 0.1mm. This means that if two objects are held less than 0.1mm apart at a distance of about 10mm from the eye, the eye is not able to detect them as separate objects. The use of the microscope increases this resolution to about 0.01mm. Alternatively, we may say that a magnifying lens enhances our resolving power by a factor of 10.

Unfortunately, several factors make it possible to magnify an object without necessarily increasing the eye’s resolution. In such situations, the object edges become so blurry that the eye is unable to detect the two objects as separate. This is the knowledge that is used to test for eyesight problems. A standard eye chart makes it possible for one to see the increased object size yet one may be unable to tell which number is projected. The resolution power of a lens is often limited. The resolution of a lens is fixed. To increase the resolution, one needs to change the lens.

It is, therefore, noteworthy that the most important property of a lens is its resolution, contrary to popular belief. A good microscope will magnify an object up to 40 times its size. However, only a quality lens will enable you to see more details than you would with a magnifying lens (Zenhausern, O’Boyle, & Wickramasinghea, 2001).

The resolution of a lens may be determined using the relationship between resolution and range. The resolution of a lens is inversely related to the distance. The resolution can be enlarged in three ways. First, it may be increased by raising the angle of light incidence by altering the design or location of the substage condenser. Second, the resolution of the lens may be increased by using specially manufactured lens and changing the medium through which the light travels each by using immersion oil. Thirdly, the resolution may be increased by lowering the wavelength of the light being used. It is best to incorporate all three methods to maximize the resolution of a microscope. The most effective method when used independently, however, is the decrease of the wavelength of light (Karrai & Grober, 1995).

For regular field microscopy, the visible light range is more convenient. Blue light has the lowest wavelength in the visible light region and is often incorporated in even the least expensive microscopes. The blue light filter is usually labeled the daylight filter. More expensive microscopes usually alter the light source to enhance the light quality hence correcting lens aberrations that arise with the design.

Resolutions can also be improved by using UV light that is usually done using electrons. The UV light has a low wavelength and, therefore, increases the wavelength. Electrons and UV light cannot be seen using the naked eye. To solve this problem, photography and fluorescent screens are used. When these are used, an electron microscope is born.

To attain maximum resolution, the microscope must be corrected for issues of lens design. Modern optical microscopes are not single lenses, but a system of lenses assembled to maximize the resolution of the microscope and minimize spherical and chromatic distortions of the image (Kohler, 1971).

Legitimate utilization of a microscope requires that the optics and light source be adjusted on the optical plane. The greater part of the rectifications for distortions relies upon fitting arrangement of the magnifying lens parts. There are two general strategies utilized for fitting arrangement of the magnifying instrument. The principal, and maybe best, is known as critical illumination. In this process a picture of the source of light is extended into the plane of the item, accordingly superimposing the light source onto the object. It has an impediment, however, in that it requires a level even light source, not so much possible with a tungsten filament bulb.

Other than being used for magnifying objects and increasing the details that can be seen, the microscope may be used for illumination and reflection. This increases the visibility of an object. It has become one of the most apparatus in the sciences laboratory (Kohler, 1971).

Conclusion

In conclusion, the optical microscope is one of the most important instruments in the science laboratories. It has been developed continuously formed from the lens. Scientists discovered that a system of lenses highly increased the size of an object. They, therefore, improved the instrument over time to the current tool. The most important breakthrough in the discoveries made using the light microscopes was the discovery of the cell. Till then, however, there has been further investigation into the cell. This investigation has been able to observe deeper into the cell to identify parts of the cell. The wavelength of light is the only thing that limits the current microscope.

References

Karrai, K., & Grober, R. D. (1995). Piezoelectric tip-sample distance control for near field optical microscopes. Applied Physics Letters. doi:10.1063/1.113340

Kohler, R. (1971). The background to Eduard Buchner’s discovery of cell-free fermentation. Journal of The History of Biology.

Petran, M., Hadravsky, M., Egger, M. D., & Galambos, R. (1968). Tandem-Scanning Reflected-Light Microscope. Journal of The Optical Society of America.

Zenhausern, F., O’Boyle, M. P., & Wickramasinghea, H. K. (2001). Apertureless near-field optical microscope.