A microscope is a scientific instrument used to view small objects. They are usually used to see details that are too small or not visible with the naked eye.
Types of Microscopes
A bright field microscope is one of the most widely used microscopes. The image is darker than the illuminated field and is made by transmitting light through the specimen.
A dark field microscope is similar to the bright field microscope but instead of a dark image on a light illuminated field, the image is bright on a dark illuminated field. A bright field microscope can be adapted into a dark field microscope by adding a stop to the condenser.
A phase contrast microscope can be used with live specimen and produces an image where the specimen contrasts with a gray background. It can be used to view internal cell details.
A differential-interference microscope produces a colorful three-dimensional image and has two prisms which add contrasting colors to the image.
A transmission electron microscope (TEM) uses electron beams to form the image. It can magnify images up to 100,000X and works by transmitting electrons through the specimen.
Like the transmission electron microscope, a scanning electron microscope (SEM) creates very detailed 3D images of the specimen and can magnify up to 650,000X. It works by sending electrons to the specimen and detecting the deflected electrons.
A fluorescence microscope uses ultraviolet light to make the image which comes out as a colored image against a black field. A confocal microscope also uses ultraviolet light to make the image.
Light Compound Microscope
The light compound microscope is one of the most common types of microscopes.
Parts of a Light Compound Microscope
- Ocular: This part of a microscope magnifies the image formed by the objectives. It is the part where the viewer looks through to see the image.
- Nosepiece: Holds the objectives and is located below the arm and the body tube.
- Base: Supports the microscope and acts as a foundation.
- Objectives: Lenses that form the first image (before the ocular) by receiving light from the field of view.
- Arm: Connects to the base and holds up the ocular, body tube, objectives, and nosepiece.
- Body Tube: The tube between the ocular and the nosepiece/objectives.
- Coarse adjustment: Used to adjust the microscope in lower power.
- Fine adjustment: Used to adjust the microscope in high power or for fine tuning.
- Stage: Supports the slide and specimen when being viewed.
- Stage clips: Clips on the stage that hold the slide in place.
- Illuminator: A source of light, usually located below the stage. A lumarod (rod that collects light) is sometimes used as a source of light in microscopes that do not use electric power.
- Diaphragm: Controls the amount of light reaching the specimen.
Principles of Microscopy
Appearance & Movement of Objects
In a microscope, objects appear upside-down and backwards. If a specimen were to move forward and right, it would appear to move backward and left when viewed through a microscope.
Magnification and Changing Objectives
The total magnification is found by multiplying the magnification of the ocular and the objectives. For example, if the ocular of a microscope is 10x and the objectives are on 12x, the total magnification would be 10 times 12, which is 120x total magnification. On a normal microscope, the ocular is usually 10x or 12x, while the objectives are about 5x for scanning, 10x or 12x for low power, and 40x-45x for high power.
When changing objectives to a higher power/magnification (scanning to low to high), the size of the field of view decreases and the field of view gets darker. The resolution (sharpness of image) and size of the image increase. The working distance decreases and the depth of focus is reduced.
The smallest measurement on a metric ruler is usually a millimeter (mm). One millimeter is equal to 1000 micrometers (mcm or μm). One micrometer is equal to 1000 nanometers (nm).