Nonimaging optics

The aperture iris diaphragm controls the angular aperture of the cone of light from the condenser, while the field iris diaphragm controls the area of the circle of light illuminating the specimen.

His method ensures every lens is positioned correctly to provide perfectly even light through the sample and into the field of view.

Criticalillumination

In 1893, Kohler added an extra lens to the microscopes of his time, changing the configuration so that light passing through the sample was uniform and no longer shadowed by the microscope’s light source (for example, a light bulb or lamp filament).

To allow a microscope to be set up for Koehler, it must have two adjustable iris diaphragms: the aperture iris diaphragm at the substage condenser and the field iris diaphragm nearer to the lamp.

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.

While setting up Koehler illumination the first time may be a little confusing, after you have set it up once, it will be easy to repeat the process each time you use your microscope.

The method for setting up your light path properly is called Kohler illumination after August Kohler, the man who invented it.

Microscopists ­– critical for advanced microscopy techniques such as differential interference contrast (DIC) or phase contrast.

科勒照明

With practice, setting up Kohler illumination becomes second nature and will transform your imaging work. It is simply one of the most important principles of light microscopy.

You’ll have the advantages of an evenly illuminated field, a bright image without glare and minimum heating of your specimen – not to mention that it will transform your images from mediocre to publication quality (if you’re into that kind of thing).

Koehler illumination is an alignment technique that reduces stray light and glare caused by reflections inside your microscope.