Free science tool
Virtual Microscope
Use a real-feeling compound light microscope in your browser. Choose a slide, turn the revolving nosepiece to switch between the 4×, 10×, 40× and 100× oil-immersion objectives, focus with the coarse and fine focus knobs, set the light and iris diaphragm, and move the stage - with the same upside-down image and shrinking field of view as a school microscope. Free, no signup.
Revolving nosepiece (objective lens)
Stage controls (move the slide)
Slide from above
The classic first slide. Notice the e is upside down and back to front, and moving the slide one way moves the image the other way. Stain: No stain - printed ink on paper.
Microscope missions (0/7)
- Focus the letter e with the 4× objective
- Move the slide - which way does the image go?
- Switch to 10× and sharpen it with the fine focus knob
- Find a cheek cell nucleus at 40×
- Use the 100× oil lens on the blood smear
- See Robert Hooke's cork cells
- Watch a paramecium swim in pond water
How to use a microscope, step by step
- Start with the lowest-power (4×) objective in place and the stage lowered.
- Place the slide on the stage, specimen over the hole, and secure it with the clips.
- Switch on the light and open the iris diaphragm.
- Looking through the eyepiece, turn the coarse focus knob until the specimen comes into focus.
- Move the slide so the part you want is in the centre, then switch to 10× and sharpen it with the fine focus knob.
- For more detail, switch to 40× and use only the fine focus knob. Turn up the light if the view gets darker.
- For 100×, put a drop of immersion oil on the slide, turn the 100× lens into the oil, and focus with the fine focus knob.
- When you've finished, lower the stage, return to 4×, remove the slide, and wipe the oil off the 100× lens with lens paper.
Some microscopes focus by moving the body tube instead of the stage - the knobs work the same way.
Parts of a microscope and their functions
| Part | What it does |
|---|---|
| Eyepiece (ocular lens) | The lens you look through. It usually magnifies 10×. |
| Revolving nosepiece | Holds the objective lenses and turns to swap between them. |
| Objective lenses | The main lenses, closest to the slide - typically 4× (scanning), 10× (low power), 40× (high power) and 100× (oil immersion). |
| Stage and stage clips | The platform that holds the slide; clips or a mechanical stage keep it in place. |
| Stage controls | Knobs on a mechanical stage that move the slide left-right and forward-back in small steps. |
| Coarse focus knob | Moves the stage up and down quickly to bring the specimen roughly into focus. Use it only at low power. |
| Fine focus knob | Makes small, precise focus adjustments - the only focus knob to use at 40× and 100×. |
| Condenser | A lens under the stage that gathers light and focuses it onto the specimen. |
| Iris diaphragm | An adjustable opening under the stage that controls how much light passes through, changing brightness and contrast. |
| Illuminator | The built-in light that shines up through the slide (older microscopes use a mirror). |
| Arm and base | The frame. Carry a microscope by the arm with your other hand under the base. |
How microscope magnification works
Total magnification = eyepiece magnification × objective magnification. With the usual 10× eyepiece, the 40× objective gives 10 × 40 = 400×. But as magnification goes up, the field of view - the width of the circle you can see - goes down in proportion. For a typical eyepiece with an 18 mm field number, the field of view is 18 mm divided by the objective's magnification:
| Objective | Total magnification | Field of view | Good for |
|---|---|---|---|
| 4× (scanning) | 40× | 4.5 mm | Finding the specimen and seeing its overall shape |
| 10× (low power) | 100× | 1.8 mm | Groups of cells, such as onion epidermis |
| 40× (high power) | 400× | 0.45 mm | Individual cells and their nuclei |
| 100× (oil immersion) | 1,000× | 0.18 mm | Blood cell detail and bacteria |
That is why a specimen that fills the view at 40× disappears off the edge at 400×, and why you centre what you want to see before switching to a stronger lens. Use the scale bar in the simulator to estimate real sizes: a red blood cell is about 7.5 µm across, and 1,000 µm make 1 mm.
Why is the image upside down?
In a compound microscope, the objective lens forms a real image of the specimen that is upside down and reversed left to right. The eyepiece magnifies that image again but doesn't flip it back, so the view is rotated 180°. Try the letter e slide: it looks like an upside-down 'ə', and when you move the slide to the left the image moves to the right. The "slide from above" panel in the simulator shows the slide the right way up, so you can compare.
What's on the slides
Letter e (newsprint)
The classic first slide. Notice the e is upside down and back to front, and moving the slide one way moves the image the other way.
No stain - printed ink on paper. Best starting objective: 4×.
Onion epidermis
Brick-shaped plant cells with clear cell walls and a dark nucleus in each. No chloroplasts - this layer of the onion never sees light.
Iodine (stains the nuclei and cell walls brown). Best starting objective: 10×.
Human cheek cells
Flat, irregular animal cells with a dark blue nucleus near the middle. There's no cell wall - compare the outline with the onion. At 100x you can spot tiny mouth bacteria.
Methylene blue (stains the nuclei dark blue). Best starting objective: 40×.
Blood smear
Thousands of red blood cells - discs about 7.5 µm across with a pale centre. Look for the occasional white blood cell with a purple nucleus, and tiny purple platelets. Use 100x with oil.
Wright's stain (red cells pink, white-cell nuclei purple). Best starting objective: 40×.
Leaf underside (stomata)
Wavy, jigsaw-like epidermal cells and pairs of bean-shaped guard cells around tiny pores - the stomata that let carbon dioxide in and water vapour out.
No stain - a peel of the lower leaf surface. Best starting objective: 40×.
Cork (Robert Hooke's 'cells')
Tiny empty compartments with thick walls. Looking at cork in 1665, Robert Hooke called these spaces 'cells' - the origin of the word. The cells are dead; only their walls remain.
No stain - a thin slice of cork. Best starting objective: 10×.
Pond water (live)
A living sample: slipper-shaped paramecia swimming with their cilia, green Spirogyra filaments with spiral chloroplasts, and golden diatoms. Real paramecia swim about a millimetre a second - they're slowed down here so you can follow them.
No stain - a living wet mount. Best starting objective: 10×.
Frequently asked questions
How does this virtual microscope work?+
It simulates a compound light microscope in your browser. The specimens are drawn at their real sizes, and the simulator models the optics a real microscope has: total magnification (eyepiece × objective), a field of view that shrinks as magnification rises, depth of focus that gets shallower at high power, light that dims at higher magnification, the need for immersion oil at 100×, and an image that is rotated 180°.
What magnification do you need to see cells?+
Plant cells such as onion epidermis are visible at 100× total magnification (the 10× objective). To see individual cells and their nuclei clearly - like cheek cells - use 400× (the 40× objective). Bacteria and the detail of blood cells need 1,000× with the 100× oil-immersion objective.
Why do you always start with the lowest magnification?+
The 4× objective has the widest field of view and the greatest depth of focus, so it is far easier to find the specimen and get it roughly in focus. Once it is centred, you move up to higher power and fine-tune with the fine focus knob.
Why is the image in a microscope upside down?+
The objective lens forms a real image that is upside down and reversed left to right. The eyepiece magnifies that image without flipping it back, so what you see is rotated 180°. That's why the letter e looks like an upside-down 'ə', and why moving the slide left makes the image move right.
Why does the 100× objective need immersion oil?+
At 100× the lens is collecting light from a very small area at steep angles. Without oil, that light bends as it passes from the glass slide into air and much of it misses the lens, so the image is dim and blurry. Immersion oil has nearly the same refractive index as glass, so the light continues straight into the lens.
Is the virtual microscope free?+
Yes - it is completely free, needs no signup and runs in any modern browser on a computer, tablet or phone. Teachers are welcome to share the link with their classes.
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