Microscopes use lenses to magnify small objects, making them visible to the human eye. They work by manipulating light (in light microscopes) or electrons (in electron microscopes) to create a magnified image.
How Light Microscopes Work
A compound light microscope, the most common type, uses two lenses to achieve high magnification:
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Objective Lens: This lens is positioned close to the specimen. Light passes through the specimen and into the objective lens. The objective lens creates a magnified, real, and inverted image. This image is projected to a plane called the intermediate image plane. (As described in the Cornell University resource).
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Eyepiece Lens (Ocular Lens): The intermediate image is then magnified further by the eyepiece lens, which you look through to view the final, magnified image. Think of it as a two-stage magnifying process, similar to taking macro shots with a camera. (As explained in the Reddit ELI5 thread).
The total magnification is the product of the magnification of the objective lens and the eyepiece lens. For example, a 10x objective lens and a 10x eyepiece lens produce a 100x total magnification. Simple microscopes of the past could magnify up to 266x. (Per the Cornell University resource on microscope lenses).
Types of Light Microscopes
Several types of light microscopes exist, each designed for specific applications:
- Compound Light Microscope: The most common type, using two lenses for magnification.
- Stereo Microscope (Dissecting Microscope): Provides a three-dimensional view, useful for examining larger specimens.
- Confocal Microscope: Uses lasers and pinholes to create sharp images of thick specimens, eliminating out-of-focus light. The objective lens and pinhole are "conjugate points" (Emory University Physics Department).
How Electron Microscopes Work
Electron microscopes use beams of electrons instead of light. They achieve far higher magnifications than light microscopes, allowing visualization of structures at the nanometer scale. Because the wavelength of electrons is much smaller than that of light, much greater resolution is possible.
Types of Electron Microscopes:
- Transmission Electron Microscope (TEM): Electrons pass through a very thin specimen.
- Scanning Electron Microscope (SEM): Electrons scan the surface of a specimen, creating a detailed three-dimensional image.
The use of electrons allows for a much higher resolution than is possible with a light microscope. However, electron microscopes require specialized preparation techniques for samples and are more complex to operate.
Conclusion
Microscopes are essential tools in various scientific fields, providing the ability to visualize structures invisible to the naked eye. Their workings are based on manipulating light or electron beams to create magnified images of specimens.
