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How to Use Kohler Illumination in Microscopy Studies

When you look at something under a microscope, the intensity and distribution of light must be clear and equal. Otherwise, you will not be able to study all aspects of the specimen. The notes you make about your observation will not be valid. It is true that you will still be able to see a good number of parts of the specimen but the shadows or yellow sheen created by a substandard illumination will most likely affect your observations negatively. This was the problem of scientists before. Thankfully, a German professor named August Köhler came up with a revolutionary way to illuminate objects in a sample plane. He invented the Kohler illumination in 1893.

Answering Questions That Led To A New Way of Doing Things

August Köhler was doing his graduate studies when he discovered the new way to illuminate objects on the sample plane of microscopes. At that time, there were many methods used to brighten objects under the microscope. One involved using gas lamps. Another mirrors. When they finally used bulbs, the filament of the bulb they used was visible in their microscope's sample plane. Needless to say, these methods were not satisfactory.

By trying to come up with solutions on various microphotography problems, August Köhler was able to invent the Kohler illumination. But it was not until he was hired by the company Carl Zeiss AG that his invention was truly given enough attention. Until today, Kohler illumination is still used. It has also been the basis for the more modern method of microscope illumination.

How to Set Up Kohler Illumination

This system needs a bulb with high density illumination, field diaphragm, condenser diaphragm, collector lens, and condenser lends. The first thing that you need to do is to set up your specimen. Close the field diaphragm until you see its edges. The edges will be blurry at this point. Now turn the condenser knobs to make the edges as clear as possible. Then center the image of the closed field diaphragm. Do this by using the condenser-centering screws. After that, you open the field diaphragm just a little bit to bring its edges out of the field of view. Then adjust the condenser diaphragm to adjust your sample's contrast. If the light is too intense, you may have to adjust it. The best way to do this is to use the proper filters. It is not advisable to reduce the power supply as this will give the sample a yellowish or brownish look. Once these steps are followed, you will be able to enjoy sample analysis without any light interference. Your experiment or observations will not have shadows or uneven lighting.

If these steps don't work, your lens probably need cleaning. Dirt in the lens and other parts of the microscope will greatly affect the quality of your image. If you still do not see a well-illuminated sample, you may have to do the steps again to check if you did them properly.

CanScope - complete solution for all your microscopy needs.
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About the Author

Do you want to set up
Kohler illumination
on your microscope? Visit CanScope.ca for the components needed. They also have many kinds of microscope, such as the
metallurgical microscope
and the
fluorescent microscope
that may be useful for your research.

Unit Membrane Model of membrane structure question?

In the 1950s, J. D. Robertson reported that all the membranes he observed in the electron microscope looked the same. This led to his proposal of the unit membrane model of membrane structure suggesting that all membranes were exactly alike. Why was this model eventually rejected?

In 1966, Lenard and Singer noted that over 30% of membrane proteins were twisted into an alpha helix. This made it likely that there were many spherical proteins.
http://www.cytochemistry.net/Cell-biology/membrane_intro.htm

Basic Membrane Architecture
The purpose of this presentation will be to show how membranes are studied by the cell biologist. First, we will look at basic unit membrane architecture. All membranes contain proteins and lipid. However, the proportion of each varies depending on the membrane. For example:

Myelin, which insulates nerve fibers, contains only 18% protein and 76% lipid. A electron micrograph of myelin is to the right.
Mitochondrial inner membrane contain 76% protein and only 24% lipid.
Plasma membranes of human red blood cells and mouse liver contain nearly equal amounts of proteins (44, 49% respectively) and lipids (43, 52% respectively).

Gut bacteria gene complement dwarfs human genome
By Andrew Bennett Hellman Researchers have unveiled a catalogue of genes from microbes found in the human gut. [More]

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