A Microscope: Definition, History and Types

The Compound Microscope

Parts of Microscope 

What is a microscope? 

A microscope is a scientific instrument that is used to magnify and observe objects that are too small to be seen with the naked eye. It typically consists of an optical system that uses lenses or mirrors to bend and magnify light, allowing the user to view the object under examination with greater clarity and detail. Microscopes are used in various fields of science, including biology, medicine, chemistry, physics, and materials science, as well as in industrial and research settings.

History: 

Historians credit the invention of the compound microscope to the Dutch spectacle maker, Zachariah Janssen, around the year 1590. The compound microscope uses lenses and light to enlarge the image and is also called an optical or light microscope. The simplest optical microscope is the magnifying glass and is good to about ten times (10X) magnification.

Different types of Microscopes.

1. Compound Microscope: High magnification for thin, transparent specimens.
2. Stereo Microscope (Dissecting Microscope): Lower magnification for larger objects in 3D.
3. Digital Microscope: Captures images digitally for convenient analysis and sharing.
4. Stereo Zoom Microscope: Variable magnification levels for tasks that require flexibility.
5. Polarizing Microscope: Studies materials with polarization effects.
6. Fluorescence Microscope: Visualizes fluorescent specimens.
7. Electron Microscope (TEM and SEM): High magnification and resolution for nanoscale imaging.
8. Confocal Microscope: Creates sharp, high-contrast images of thick specimens.
9. Phase Contrast Microscope: Enhances contrast of transparent specimens.
10. Darkfield Microscope: Provides high contrast for unstained or transparent specimens.
11. Digital Holographic Microscope: Captures holograms for 3D imaging and measurements.
12. Atomic Force Microscope: Scans surface of specimens at atomic scale for surface topography and properties.

The compound microscope has two systems of lenses for greater magnification, 

1) The ocular, or eyepiece lens that one looks into and 

2) The objective lens, or the lens closest to the object. Before purchasing or using a microscope, it is important to know the functions of each part.

1. Eyepiece Lens: the lens at the top that you look through. They are usually 10X or 15X power.
2. Tube: Connects the eyepiece to the objective lenses
3. Arm: Supports the tube and connects it to the base. It is used along with the base to carry the microscope
4. Base: The bottom of the microscope, used for support
5. Illuminator: A steady light source (110 volts) used in place of a mirror.
6. Stage: The flat platform where you place your slides. Stage clips hold the slides in place. Revolving Nose-piece or Turret: This is the part that holds two or more objective lenses and can be rotated to easily change power.
7. Objective Lenses: Usually you will find 3 or 4 objective lenses on a microscope. They almost always consist of 4X, 10X, 40X, and 100X powers. When coupled with a 10X (most common) eyepiece lens, we get total magnifications of 40X (4X times 10X), 100X, 400X, and 1000X.The shortest lens is the lowest power. The longest one is the lens with the greatest power. The high-power objective lenses are retractable (i.e. 40XR). This means that if they hit a slide, the end of the lens will push in (spring loaded) thereby protecting the lens and the slide.
8. Rack Stop: This is an adjustment that determines how close the objective lens can get to the slide. It is set at the factory and keeps students from cranking the high-power objective lens down into the slide and breaking things.
9. Diaphragm or Iris: Many microscopes have a rotating disk under the stage. This diaphragm has different-sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide. Thereby is no set rule regarding which setting to use for a particular power rather, the setting is a function of the transparency of the specimen the degree of contrast you desire, and the particular objective lens in use.
10. Coarse adjustment: This is used to focus the microscope. It is always used first, and it is used only with the low
11. Fine adjustment: This is used to focus the microscope. It is used with the high­ power objective to bring the specimen into better focus.

The Compound Microscope

How to Focus Your Microscope?: 

• The proper way to focus a microscope is to start with the lowest power objective lens first and while looking from the side, crank the lens down as close to the specimen as possible without touching it. 
• Now, look through the eyepiece lens and focus upward only until the image is sharp. If you can’t get it in focus, repeat the process again. Once the image is sharp with the low-power lens, you should be able to simply click on the next power lens and do minor adjustments with the fine adjustment knob. 
• If your microscope has a fine focus adjustment, turning it a bit should be all that’s necessary. Continue with subsequent objective lenses and fine focus each time. Note: Both eyes should be open when viewing through the microscope. 
• This prevents eye fatigue, which occurs when the non­ viewing eye is kept close keeping both eyes open does take some practice, but it is highly recommended also, you should never let your eye touch the ocular lens. 
• If your eyelashes touch the lens you are too close. Always remove eyeglasses when viewing through a microscope. If your eyeglass lens touches the microscope it may get scratched.