A light microscope lets you see cells, tissues, and tiny organisms that are too small to view with the unaided eye. It uses visible light, glass lenses, and careful focusing to make a magnified image. Learning to use a microscope well matters because many biology observations depend on clear, accurate viewing.
Good technique also protects the slide, the lenses, and the specimen.
Key Facts
- Total magnification = eyepiece magnification x objective lens magnification.
- If the eyepiece is 10x and the objective is 40x, total magnification = 10 x 40 = 400x.
- Resolution is the ability to distinguish two close points as separate.
- Start focusing with the lowest power objective and the coarse focus knob.
- Use the fine focus knob at high power to sharpen the image without damaging the slide.
- Field of view decreases as magnification increases.
Vocabulary
- Eyepiece
- The lens you look through, usually with a magnification of 10x.
- Objective lens
- A lens near the specimen that provides the main magnification, such as 4x, 10x, or 40x.
- Stage
- The flat platform that holds the slide in place under the objective lens.
- Resolution
- The ability of a microscope to show two nearby points as separate details.
- Wet mount
- A temporary slide made by placing a specimen in a drop of liquid under a coverslip.
Common Mistakes to Avoid
- Starting on high power, which makes the specimen hard to find and increases the risk of hitting the slide with the objective lens.
- Using the coarse focus knob on high power, which can move the lens too far and crack the slide or damage the objective.
- Forgetting to calculate total magnification, which leads to reporting only the objective power instead of the actual viewing magnification.
- Trapping air bubbles under the coverslip, which can look like cells and block a clear view of the specimen.
Practice Questions
- 1 A microscope has a 10x eyepiece and a 40x objective lens. What is the total magnification?
- 2 At 100x magnification, the field of view is 1.8 mm wide. About how many 0.3 mm long cells could fit across the diameter of the field of view?
- 3 Explain why a student should begin focusing a slide with the lowest power objective before switching to higher magnification.