Parts of a Microscope and Their Functions
A microscope makes small things big enough to study, but it only works properly if you know which knob does what. Below is a labelled diagram of a compound microscope, a table of what each part does, and the differences between the types you will meet in a South African classroom or lab.
Parts of a microscope and their functions
| Part | What it does |
|---|---|
| Eyepiece (ocular lens) | The lens you look through, usually 10x. Magnifies the image a second time. |
| Body tube | Carries the image from the objective up to the eyepiece. |
| Revolving nosepiece | Turns to swap between objective lenses. It should click into place. |
| Objective lenses | The lenses closest to the specimen, commonly 4x, 10x, 40x and 100x oil. They do the real magnifying. |
| Stage | The platform the slide sits on. Plain stages use clips, mechanical stages move the slide with knobs. |
| Stage clips | Hold the slide still so it does not shift while you focus. |
| Condenser | Gathers light and aims it up through the specimen. |
| Iris diaphragm | Opens and closes to control how much light reaches the slide, which sets your contrast. |
| Illuminator | The light source: an LED, a halogen lamp, or a mirror on older models. |
| Coarse focus knob | Moves the stage a long way to find the specimen at low power. |
| Fine focus knob | Moves the stage a tiny amount to sharpen the image at high power. |
| Arm | The curved back of the microscope. Carry it by the arm, with your other hand under the base. |
| Base | Takes the weight and keeps everything steady. |
The lenses
Two sets of lenses do the magnifying. The objectives sit millimetres above the slide and are marked with their power: 4x, 10x, 40x, sometimes 100x. The eyepiece, almost always 10x, magnifies whatever the objective hands it. Multiply the two and you get your total magnification, so a 10x eyepiece with a 40x objective shows the specimen at 400x.
The 100x objective is different. It only works with a drop of immersion oil between the lens and the slide, because the oil stops light bending away as it crosses the air gap. Use it dry and you get a dim, cloudy view no amount of focusing will fix.
The stage
A plain stage holds the slide under two metal clips, and you nudge the slide by hand. That is fine at 40x and 100x. Once you go past 400x, a fingertip nudge sends the specimen out of view entirely, which is why a mechanical stage matters: two knobs slide the slide left to right and back to front, a fraction at a time. Some stages add vernier scales, small numbered rulers that let a learner record exactly where something was and find it again next lesson.
The light
Older microscopes use a mirror to bounce daylight up through the specimen, which still works and needs no power at all. Most modern models use an LED, and some run on batteries, which matters when the power goes out mid practical. Between the light and the slide sits the condenser with its iris diaphragm. Beginners usually leave the diaphragm wide open and wonder why a pale specimen looks washed out. Closing it down is what makes the edges of a cell visible.
Focus and frame
Coarse focus finds the specimen. Fine focus sharpens it. The rule that saves slides: start at the lowest power, focus with the coarse knob, then move up through the objectives using only the fine knob. The arm and base are the structure, and they are also how you carry the thing. Not by the head, and never by the stage.
What is a microscope?
A microscope is an instrument that magnifies objects too small for the naked eye. In a school or lab that usually means cells, tissue sections, microorganisms, pond water, crystals or fibres. A light microscope does the job with glass lenses and a lamp. Light passes through a thin specimen, the objective lens bends that light to form an enlarged image, and the eyepiece enlarges it again before it reaches your eye.
There is a practical ceiling to this. Around 1000x, a light microscope stops resolving new detail no matter how much more you magnify, because visible light itself has a wavelength. That is why a bigger number on a box is not automatically a better microscope. A 2000x claim on a model with no oil immersion lens is empty magnification: a larger, blurrier version of the same image.
Types of microscope
Compound microscopes are the standard school and lab instrument. Two sets of lenses, a slide on the stage, light from below, 40x to 1000x. Everything in the diagram above describes a compound microscope. Browse compound microscopes if this is what you need.
Stereo microscopes work at much lower power, roughly 10x to 50x, and show a three dimensional view of whole objects rather than thin slices. Insects, seeds, rock samples, circuit boards, anything you want to dissect or repair while looking at it. See stereo microscopes.
Digital microscopes put a camera where the eyepiece would be, or add a screen, so a class can see the same specimen at once instead of queueing. See digital microscopes.
Electron microscopes replace light with a beam of electrons and reach magnifications far beyond anything optical. They are research instruments, priced accordingly, and no school lab has one.
Compound microscopes are also sorted by how many eyepieces they have: monocular (one), binocular (two, easier over a long practical) and trinocular (two plus a camera port).
How to use a microscope
- Put it on a level bench, carried with one hand on the arm and one under the base.
- Turn the nosepiece to the lowest objective, usually 4x, until it clicks.
- Clip the slide onto the stage with the specimen over the hole in the middle.
- Switch on the light and open the diaphragm about halfway.
- Use the coarse focus to bring the specimen into view, then the fine focus to sharpen it.
- Move up to the next objective. Re-sharpen with the fine focus only.
- Adjust the diaphragm until you can see edges clearly, then centre what you want before going higher.
Common problems and what causes them
Everything is dark. The diaphragm is closed too far, or the objective is not clicked into place.
The image is bright but washed out. The opposite problem: too much light for a pale specimen. Close the diaphragm gradually until detail appears.
It focuses at 100x but not at 400x. Either the slide is upside down, or you are past the focal point. Go back to low power, refocus, and work up again.
The view at 1000x is dim and smeared. The 100x objective needs immersion oil. Clean the lens with lens tissue afterwards, every time.
Blurry patches that move when you move your eye. That is dirt on the eyepiece, not on the slide.
Frequently asked questions
What are the main parts of a microscope?
A compound microscope has twelve parts worth knowing: the eyepiece, body tube, revolving nosepiece, objective lenses, stage, stage clips, condenser, iris diaphragm, illuminator, coarse focus, fine focus, arm and base. The eyepiece and objectives do the magnifying. Everything else holds the slide still, lights it and brings it into focus.
What is the function of the eyepiece?
The eyepiece is the lens you look through, and it magnifies 10x on most school microscopes. It takes the image the objective lens has already enlarged and enlarges it again, which is how a 10x eyepiece and a 40x objective end up showing you 400x.
What is the difference between coarse and fine focus?
The coarse focus moves the stage a long way and is used to find the specimen at low power. The fine focus moves it a fraction of a millimetre to sharpen the image. At 400x and above, use the fine focus only, because the coarse knob will drive the lens into the slide.
What does the condenser do on a microscope?
The condenser is the lens under the stage. It gathers light from the illuminator and aims it into a cone through your specimen. The iris diaphragm built into it opens and closes to control how much light gets through, which is what gives you contrast on a pale specimen.
How do you work out total magnification?
Multiply the eyepiece by the objective. A 10x eyepiece with a 4x objective gives 40x, with a 40x objective gives 400x, and with a 100x oil objective gives 1000x.
What is the difference between a light microscope and an electron microscope?
A light microscope uses visible light and glass lenses, and reaches about 1000x. An electron microscope fires a beam of electrons instead, which reaches far higher magnification and can show viruses, but it costs many times more and needs a specialist to run it. Every microscope in a South African school lab is a light microscope.
Once you know the parts, choosing between models gets much easier. Our guide to choosing a microscope works through magnification, budget and what schools actually need, and the basics of microscope slides covers what goes on the stage. You can also browse the full range of microscopes we stock for South African schools and labs.
