Zacharias Jansen of Holland can be credited with inventing the first microscope. His microscope had two lenses, one that magnified the image and another which further magnified the image produced by the first. The lens close to the eye was a bi-convex lens and the one farther from the eye was a plano-convex lens. These two lenses were mounted on two tubes which were placed in such a way that sliding one of the tubes altered the focus of the microscope.
In 17th century, Anton von Leeuwenhoek and Robert Hooke researched more on this subject and they discovered that to increase the magnification power of the microscope, the focal length had to be reduced. Leeuwenhoek's microscope was a single glass lens, whereas Robert Hooke's was a compound microscope having two lenses. With time, high quality lenses were used in microscopes and both, magnification power and resolution improved. Magnification and resolution are the two factors that determine the quality of a microscope. Magnification is the degree to which a sample is magnified when placed under a microscope. The light microscope magnification is calculated as
Magnification = Objective lens × Eyepiece lens
Resolution is the ability to distinguish between two tiny objects or a measure to which we get a detailed image.
Light Microscope Parts and Functions
Eyepiece lens: This is the lens from where you look at the image. The power of these lenses is around 10x.
Tube: The tube connects the eyepiece to the objective lenses. We will know about objective lenses later on.
Illuminator: To observe the specimen carefully, natural light may not be sufficient, so a microscope has a small bulb and the light from this bulb is redirected on the specimen by the means of a mounted mirror.
Base: The base is used to stabilize the microscope and makes it easy to move the microscope from one place to another.
Objective lens: The objective lenses are attached to the end of the tube. Normally, three to four objective lenses can be found in a microscope. The magnifying power of these lenses is in the range of 4X to 100 X.
Diaphragm: A diaphragm is used to alter the intensity of light projected on the interface.
Adjustment Knobs: The adjustment knobs help in observing the specimen in a better way, that is, they enable the user to get a highly magnified image. There are two adjustment knobs in a microscope. A coarse adjustment knob and a fine adjustment knob. The coarse adjustment knob helps in bringing the specimen in the right plane of focus, whereas the fine adjusting knob helps in clarifying a partially focused image.
Electron Microscope
Light microscopes are the oldest microscopes that are still being used, but the advances in science and technology has fueled the human desire to know more about his/her environment. There are certain organisms that are so small that they cannot be seen under a light microscope. To observe these organisms, an electron microscope is used. An electron microscope has a better resolution and greater magnifying power as compared to a light microscope. There are some differences between a light microscope and an electron microscope, let us take a look at them.
Light Microscope vs Electron Microscope
| S.no. | Light Microscope | Electron Microscope |
| 1 | Affordable ($150 to $800) | Expensive (More than $1 50,000) |
| 2 | Easy to operate and carry | Requires expertize to use |
| 3 | Easy sample preparation | Sample preparation takes time |
| 4 | Original color of sample is maintained | Images are produced in black & white |
| 5 | Samples used can be living or dead | Only dead samples are used |
| 6 | Magnification power is 2000X | Magnification power is over 500,000X |
