- What is an inverted microscope?
- What are the types of the inverted microscope?
- How are inverted microscopes constructed?
- What are the parts of an inverted microscope?
What is an inverted microscope?
An inverted microscope is a type of microscope that comprises a light source with a condenser on top, placed above the microscope stage pointing downwards, and a set of objective lenses placed below the stage pointing upwards. This microscopic design was invented by J. Lawrence Smith in 1850 at Tulane University ( previously known as the Medical College of Louisiana). These microscopes were mainly used for examining medical samples.
What are the types of the inverted microscope?
Inverted microscopes can be of two types: biological inverted microscopes and metallurgical inverted microscopes.
Metallurgical inverted microscopes are used for observing and inspecting several types of mechanical parts over a very high magnification. In this, the smooth side of the sample is placed on the stage directly. This smooth surface is made by polishing and is known as a puck. These microscopes are in the fractography process for detecting fractures.
Biological inverted microscopes are used for examining living biological samples. These microscopes are designed to provide a magnification of about 40x, 100x, and sometimes 200x and 400x. Biological microscopes differ from metallurgical microscopes as in this the sample is placed on a Petri dish and not directly on the stage. These microscopes are specially used for developmental biology, in-vitro fertilization, cell biology, live-cell imaging, neuroscience, and microbiology.
How are inverted microscopes constructed?
In the case of inverted microscopes, the microscope stage is generally fixed. The sample is focused by adjusting the level of the objective lens vertically with the help of focus knobs. Inverted microscopes typically have four to six different microscope objective lenses depending on their size. These lenses are fitted in the revolving turret or nosepiece and can be changed by the user. Advanced inverted microscopes are fitted with confocal scanning, video cameras, fluorescence illumination, and several other devices.
What are the parts of an inverted microscope?
A modern day microscope has the following structural components:
Eyepiece (ocular lens):
The eyepiece is one of the main parts of a microscope from where the sample object’s image can be seen. It is essentially a cylindrical tube with one or more lenses inserted at the bottom of the tube. It is a part of the ocular lens and prevents the ocular lens from falling or experiencing damage. It also improves the clear view of the lens. Microscope eyepieces can be changed according to the required magnification. The most commonly used value of eyepiece magnification is 5x, 10x, 15x, and 20x.
Objective turret, revolver, or revolving nose piece:
Objective turret, revolver, or revolving nose piece refers to the part of the microscope that holds the objective lenses and allows the user to rotate or switch the objective lenses according to their requirements.
The objective lens is placed at the lower end (below the stage) of the microscope tube directed towards the object that is to be observed. There may be one or more objective lenses for a microscope. The objective lens collects light from the sample object. Microscope objective lenses are designed to be parfocal i.e. the sample object remains in focus even when we switch the lenses. Objective lenses are selected according to the magnification and numerical aperture of the lens.
The most commonly used objective magnifications range from 5x to 100x and corresponding numerical apertures range from 0.14 to 0.7. The higher the magnification higher is the numerical aperture. Some high-performing microscopes use matched objective and eyepiece lenses for better performance.
Focus knobs are used for adjusting the objective focus up and down. This is especially helpful for adjusting the focus for a specimen of varied thickness. There are two types of focus knobs- Coarse adjustment: Coarse adjustment knob is used for adjusting the focus for a specimen significantly and Fine adjustment: Fine adjustment is used for adjusting the focus for specimen minutely.
The stage provides a platform for placing the specimen below the objective lens for viewing. The stage illuminates or passes light to the specimen via a transparent circle on which the specimen slide is placed. The stage also has a set of arms for securing the slide on which the specimen is placed. These slides generally have a dimension of 25 x 75 mm. These arms can be adjusted finely to ensure the slide is securely placed for different microscope objectives. In modern-day microscopes, the stage is movable and can be adjusted up and down.
Microscope light sources can be of several types. Advanced microscopes have artificial lighting sources fitted above the microscope stage for illuminating the sample. The intensity and brightness of such light sources can be adjusted manually based on the user’s requirements. The light source may be a halogen lamp, an LED, or a laser. More expensive microscopes use Köhler illumination as a light source.
Some examples of samples observed via an inverted microscope:
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