Light microscope uses light as a medium to transmit an image to our eyes. They have been around for a long time, and have gone through various improvisations.
Light microscope is an instrument that is used to observe small organisms that are not visible to the human eye. They are called so, because they rely on light to produce an image. They are of various types; some simple ones, like the one you have in your laboratory, or the more complex ones which are used by biologists. Magnification and resolution are two of its important features.
Zacharias Jansen of Holland can be credited with inventing the first microscope. His device 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.
In the 17th century, Anton von Leeuwenhoek and Robert Hooke, researched more on this subject and they discovered that to increase the magnification power, the focal length had to be reduced. Leeuwenhoek’s microscope was a single glass lens, whereas Robert Hooke’s was a compound one having two lenses. With time, high quality lenses were used, hence, magnification power and resolution were improved. Magnification and resolution are the two factors that determine its quality. Magnification is the degree to which a sample is magnified when placed under a microscope. It 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.
Parts and their 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 small bulb is present 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 device and makes it easier to move it 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 single device. 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 and refined image. There are two adjustment knobs present. 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 ones that are still being used, but the advancement 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 this device. To observe these organisms, an electron microscope is used. It has a better resolution and greater magnifying power.
| S.no. | Light Microscope | Electron Microscope |
| 1 | Affordable ($150 to $800) | Expensive (More than $1 50,000) |
| 2 | Easy to operate and carry | Requires expertise 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 |
Although the light microscope has certain limitations, it is still widely used in schools around the world.