Microscope: Uses and How to Use It
Microscope: Uses and How to Use It
A microscope is an optical instrument for viewing objects too small for the naked eye, such as cells, bacteria or tissue. A light microscope uses objective and eyepiece lenses; total magnification is their product, e.g. a 40× objective with a 10× eyepiece gives 400×.
What is a microscope used for?
- Observing plant, animal and human cells in biology practicals.
- Identifying microorganisms such as bacteria and fungi (after staining).
- Examining blood, urine or tissue samples in clinical laboratories.
- Inspecting material surfaces in materials research and quality control.
Parts of a microscope
- 1Eyepiece – lens near the eye, usually 10×
- 2Tube – connects eyepiece and objectives
- 3Nosepiece and objectives – rotated to choose 4×, 10×, 40× or 100×
- 4Stage and clips – holds the slide
- 5Condenser, diaphragm and lamp – control the amount of light
- 6Coarse and fine focus – coarse and fine focus knobs
- 7Arm – the handle used to carry it
- 8Base – supports the whole microscope
How to use a microscope
Carry it with two hands
Hold the arm with one hand and support the base with the other. Carry it upright, close to your body, and set it on a stable bench.
Place the slide on the stage
Place the slide (1) on the stage with the specimen over the light hole and secure it with the clips (2).
Start with the lowest magnification
Turn the nosepiece (1) until the 4× or 10× objective clicks into place. The specimen is easier to find at low power because the field of view is wider.
Focus: coarse knob first, then fine
Watching from the side, bring the stage close to the objective with the coarse knob. Then, looking through the eyepiece, move it away slowly until the image appears and sharpen it with the fine knob (1). With 40× and 100× objectives, use only the fine knob.
Observe with both eyes open
Keep both eyes open when looking through the eyepiece to avoid eye strain. Adjust the diaphragm if the image is too bright or lacks contrast.
Common mistakes
- Turning the coarse knob while looking through the eyepiece at high power: the lens can hit and break the slide.
- Cleaning lenses with ordinary tissue or rough cloth. Use lens paper.
- Carrying it with one hand or swinging it: the eyepiece can fall out.
Care and safety
- After use, return to the lowest objective, lower the stage, switch off the lamp and cover it.
- Wipe immersion oil off the 100× objective after every use.
Types and sizes
Common laboratory types: monocular (one eyepiece, common in schools), binocular (two eyepieces, comfortable for long use), trinocular (with a camera port) and stereo (low magnification, three-dimensional view of whole objects).
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Frequently asked questions
How do you calculate microscope magnification?
Multiply the eyepiece magnification by the objective magnification. A 10× eyepiece with a 40× objective gives 400×.
What does the diaphragm do?
The diaphragm controls how much light reaches the specimen, which affects image brightness and contrast.
What is the difference between the coarse and fine focus?
The coarse knob moves the stage a long way for rough focusing; the fine knob moves it in small steps to sharpen the image.
Related equipment
Compiled by the AMI Scientific team from standard laboratory practice. Illustrations: AMI Scientific. Updated: 06-11-2026.
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