Condenser Lens

No laboratory is complete without a microscope, an instrument that opens a whole new world of unseen organisms to us. It is used in forensic investigations, biology, and research studies, that involve a thorough examination of micro-organisms. The microscope alters the direction of the light rays, that enables a detailed view of the organism, with the help of condenser lens, which is a key part of the microscope.

The condenser lens is one of the most essential parts of a microscope, that is used to see extremely tiny objects which are otherwise invisible to the naked eye. There are different types of microscopes, such as compound microscopes, digital microscopes, optical microscopes, stereo microscopes, and electron microscopes.

Each of these microscopes come with different magnifying capacity required to observe various microscopic specimen.

In upright microscopes, the condenser is placed above the illumination source, and under the specimen. In inverted microscopes, it is placed above the stage, and below the light source. Its function is to gather light from the illumination source, and focus it in such an angle, that the specimen is highlighted.

First, the light originating from the illumination source travels through diaphragm. The diaphragm helps to adjust the intensity and angle of light, with the help of various numerical apertures. Then, the lens focuses that light on the specimen. Generally, the microscope consists of one or more lenses, along with a variable aperture diaphragm.

• Abbe: This is a simple condenser with two lenses . It was developed in 1870 and was named after its inventor, Ernst Karl Abbe. It is located below the stage of the microscope, and helps in controlling the light passing through the specimen. 

It has two controls which are used to optimize brightness, contrast, and parity of the light. Most modern light microscopes use Abbe condensers, because of its multipurpose qualities.

• Aplanatic: This type is used for correcting spherical aberrations that create imperfect and blurred image of the specimen, due to the increased refraction of light rays. Spherical aberrations cause the instrument to deviate from the norm, affecting the sharpness of the image. 

With the help of aplanatic condensers, it is possible to correct these spherical aberrations, as it controls the refraction of light beams and gives a clear image.

• Acromatic: This type is used when chromatic or optical aberrations occur, which do not allow the lens to focus all the colors of the specimen, to an equal convergence point. It gives a distorted image of the specimen. 

It happens when the lens has a different refractive index for different wavelengths of light and it can be corrected by using acromatic condenser. They are generally used in microscopes having high magnification power.

• Aplanatic and Acromatic: This type is a combination of the aplanatic and acromatic condenser lens. It is used for correcting both the spherical and optical aberrations. Instead of using them separately, it is advantageous to use them together, as it serves a dual purpose.

The purpose is to collect the light from the illumination source and brighten the specimen which is on the slide under investigation. If you need magnification power that is 400X or above, then condenser lens is more useful as it gives a better quality image of the specimen.

When you say that a microscope has 400X power, that means it magnifies the specimen 400 times bigger than the original. Lens rated 0.65 NA or greater can be advantageous, if the microscope is of a higher power.

Apart from the very important use of condenser lens in microscopes, they are also used in magnifiers, spotlights, enlargers, projectors, and photo cell systems. The lens is a crucial part of any microscope, and noticing finer details of specimens would have been impossible without it.