Virtual microscope

A virtual microscope lets you use a light microscope on a screen: choose a slide, focus it, switch objective lenses and measure what you see. Our Virtual Microscope has seven slides, from onion cells and blood to a leaf section, dividing root tip cells and live pond water, with ×4, ×10, ×40 and ×100 objectives. The blur, the field of view and the depth of focus all come from real optics, and a measuring line links actual size, image size and magnification.

It opens on onion cells at ×100 total magnification (the ×10 objective), with a measurement already drawn across them. It works on any screen, with no microscope or slides needed.

Try it

Virtual Microscope

Focus on cells and tissues and measure them with a scale bar

Open the simulatorGo to its page

How to use the virtual microscope

1. Under Slide, choose what is On the stage: onion epidermis, human cheek cells, a blood smear, a leaf cross-section, a root tip with mitosis, bacteria (Gram stain) or pond water (alive).
2. Pick the objective: ×4, ×10, ×40 or ×100. The eyepiece is ×10.
3. Bring the slide into focus with Coarse focus, then sharpen it with Fine focus. Each layer of the specimen blurs by its own distance from focus.
4. Under Light and tools, set the Lamp and the Iris diaphragm, and turn on the Eyepiece graticule if you want one.
5. Choose Move slide to drag the slide about, or Measure and drag across a cell to measure it.

The readouts give the total magnification, the field of view, the actual size you measured and the image size, I = M × A. The pond water slide moves, so it has its own play button. A view with a measurement can be saved and printed.

Magnification, field of view and resolution

The total magnification is the eyepiece power times the objective power. The numbers for each lens come straight from the microscope's optics:

The field of view is the eyepiece's field number, 18 mm here, divided by the objective power, so higher power shows a smaller area. The resolution limit, the smallest gap that can be seen as two separate points, is 0.61λ ÷ NA, using green light of 0.55 μm and each lens's numerical aperture. That is why a light microscope cannot show detail much smaller than about 0.2 μm, however much you magnify.

Worked examples

Example 1: total magnification

With the ×10 eyepiece and the ×40 objective, the total magnification is 10 × 40 = ×400. The readout shows ×10 × ×40 = ×400.

Example 2: image size, actual size and magnification

These three are linked by:

A red blood cell is about 7 to 8 μm across. At ×400, a 7.5 μm cell gives an image of 400 × 7.5 μm = 3,000 μm = 3.0 mm. Measure a cell on the blood smear and the readout gives both its actual size and its image size. Convert units first: 1 mm = 1,000 μm.

Example 3: using the eyepiece graticule

An eyepiece graticule is a scale in the eyepiece, so its units mean different lengths at each objective. At ×40, one unit is 2.5 μm. A cell that spans 24 graticule units is 24 × 2.5 = 60 μm long. In the lab you calibrate the graticule against a stage micrometer; the virtual microscope does it for you.

Try one:

Focus, light and the iris

Higher powers have a shallower depth of focus, so only a thin slice is sharp: about 55 μm at ×4 but about 1.3 μm at ×40. That is why you focus on ×4 first and then use only the fine focus at higher powers. Closing the iris diaphragm deepens the focus and raises the contrast, but dims the view and lowers the resolution. The ×100 objective uses immersion oil, which lets it gather a wider cone of light.

What the virtual microscope does not do

• A light microscope only. It cannot show what an electron microscope shows, such as ribosomes or the inside of mitochondria.
• Seven prepared slides. You cannot load your own images or prepare a new slide.
• No staining step. The slides come already stained where they would be in the lab.

Common mistakes

• Mixing mm and μm. Put image and actual size in the same unit before dividing. 1 mm = 1,000 μm.
• Adding the lens powers. Total magnification is eyepiece × objective, not eyepiece + objective.
• Confusing magnification with resolution. Magnifying a blurred image does not show more detail.
• Using the coarse focus at high power. It can crash the lens into the slide. Use the fine focus above ×10.
• Using graticule units as micrometres. A graticule unit is a different length at each objective.

Practise cell biology in a short timed paper

Microscopes and magnification come up in High School Biology and Honors Biology practice, and in GCSE Biology Higher and A-level Biology: Year 1 in the UK. Each daily paper is a short timed paper of 8 questions worth 25 to 35 marks, and the papers mix topics. Our parts of a microscope guide names each part, and the animal and plant cells guide covers what you see on the slides.

Read next

Biology · CellsMicroscope diagram: labelled parts and what they doThe labelled parts of a light microscope and what each one does, how to use it step by step, and how to calculate magnification, for GCSE Biology.