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The lack of brightness or illumination is a huge disadvantage for light microscopy. The lack of detailed visibility is surely a problem for certain specimens.
Condenser lens and illuminating mirrors are your best bet for overcoming the hurdle. In this section we will elaborate on everything that you must know about illumination.
Illumination and the Optical Terrain of a Microscope
An optical microscope is designed to ensure an organized and precise passage of light rays. Illuminating a specimen is the most critical variable to achieve high-quality microscopic imaging.
The ease with which you can manipulate illumination is highly advantageous for observations. Lack of brightness is not a disparity for simple microscopy.
There is an added presence of several optical elements with contrast enhancement techniques. Some of these include polarization contrast, fluorescence, and phase contrast.
Such a condition consumes more light. Due to the presence of an optical element, the much brightness is non-existent. This leaves behind a relatively darker image, which is not suitable for proper observation.
Upon proper adjustment, the condenser’s light fills up the objective’s focal plane. The incoming light is adequate to form high-quality images.
The condenser-aperture configuration thus controls the cone of light rays. In microscopy, it is vital to reset the settings whenever the objective changes.
A low magnifying objective will produce a more significant field of view. As the magnification is made higher, your field of view shrinks further.
There are several light sources available as illuminators for microscopy. These illuminators are used both for regular and quantitative observations.
What should you know about Illuminators?
For standard observations, you can use a routine microscope. These devices do not need any illumination for lighting up the specimens.
In some cases, these microscopes are closer to the specimen. In such a situation, there is a darkening of the image.
Or you may need to lighten up the specimen better for observing details. In line with these reasons, scopes have inbuilt lighting aids. These aids are called illuminators.
The conventional illuminators are situated in front of an external light beam. These external sources can be in the form of room light, lamplight, and natural lights.
The sources are located at the bottom of the microscope’s stage. They send light rays up, passing the specimen as transmitted light.
Typical mirror illuminators have a concave surface. The flat side is meant for light transmission.
The transmission of light helps the image to appear sharper. In contrast, the concave side concentrates these light rays. This imparts brightness to the already sharp image.
You need the right adjustments to direct a light source on a mirror illuminator. Or, in some cases, the light might just be too intense for the specimen.
To overcome this incompetence, you need illuminator with personalized bulbs and diodes. Such illuminators are rechargeable.
You can use them for either illumination or transmission or both. When you are using such a technique to illuminate objects, the temperature rises invariably.
You need to avoid overheating as this may ruin your specimens. For that purpose, heat-absorbing devices, as well as variable intensity illuminators, can be used.
For optical microscopes of the highest-powered to need to supplement the system with a condenser. A condenser lens, along with a light illuminator for transmission, is perfect for detailed microscopy.
The lenses are situated above the light source, but below the microscope’s stage. They cause the light rays to concentrate a pass accurately through the specimen efficiently.
What is a condenser lens?
The condenser lens focuses a light beam on a staged specimen. These lenses are more useful when present at higher powers such as 400x.
Supplementing your microscope with a condenser is beneficial for several reasons. This is especially true when the device is at a maximum power of 400k.
In such a case, you will reap the most out of the system with a 0.65 NA rated condenser. You will have to spend less time focusing on the specimen with a stage mounted condenser lens.
The conjugated planes in a microscope
The microscope consists of two planes. These optical planes are interconnected with each other. While one is responsible for image formation, the other helps in illumination.
Both optical planes, when combined, are known as conjugate planes. The first set of planes manipulates the path of illumination.
The second plane is meant to achieve adequate Kohler illumination. In theory, an object is focused on both the planes simultaneously.
Reflected light microscopy
Reflected is often called incident light or metallurgical microscopy. This is the preferred technique for observing specimens that turn opaque at a thickness of 30 microns.
Several specimens come under this category. Some of these include ores, ceramic, semiconductors, polymers, paint, and paper.
These specimens do not allow the proper passage of light. In such a case, the light is directed to the surface. This directed light then reflects your microscope’s objective.