Your microscope
What you see under the microscope · Blood
Blood under the microscope: red cells, white cells and platelets
A drop spread and stained on a slide. Scroll down to look at it magnification by magnification with a real microscope: choose the model, the light and the technique in the panel.
The field of view, resolution and magnifications come from each instrument's spec sheet.
40×: choosing where to look
With the 4× objective the field of view is a few millimetres across. It is used to scan the smear and find the area where the cells are not piled up. Each red blood cell is barely a dot.
100×: thousands of dots
You can now make out separate dots: each one is a red blood cell. This is the magnification for scanning the sample, not yet for seeing the shape.
400×: discs with a pale centre
The red blood cells are now discs and you can just make out their paler centre. The white blood cells stand out because their nucleus stains violet. This is the typical magnification for counting cells.
1000× with immersion oil
You can see the shape: the pale centre of the red blood cell, the lobes of the neutrophil's nucleus and the platelets, which are much smaller.
Try darkfield or phase contrast in the panel: it completely changes what you see.
Why the centre looks paler
The red blood cell is a disc that is concave on both sides: about 2.6 µm thick at the rim and 0.8 µm at the centre. More light passes through the centre, which is why it looks pale.
Shape: Evans and Fung (1972). The microscope does not give you this side view, as it sees a single plane.
Which microscope do you need to see this?
For blood you need a 100× oil-immersion objective. At 400× you count cells; at 1000× you study their shape.
Which microscope do I need?Frequently asked questions
What magnification do you need to see red blood cells?
They appear as dots at 100× and as discs at 400×. To see their shape and that of the white blood cells, 1000× is used with an oil-immersion objective.
Why does the red blood cell have a paler centre?
Because it is a disc that is concave on both sides: it is thinner at the centre than at the rim, and more light passes through the centre.
What is immersion oil?
An oil placed between the sample and the 100× objective. It allows a numerical aperture greater than 1 and, with it, you can see details of a few tenths of a micron.
Can you look at blood in darkfield?
Yes: with a mirror darkfield condenser (cardioid) and a 100× oil objective with iris, the blood cells shine against a black background. It comes as a standard configuration on some biological microscopes.
How this simulation is made
It is not a photograph: it is a calculated model. Magnification, field of view and resolution come from each microscope's spec sheet; the sample measurements come from the sources cited below.
| What | How it is calculated | What is approximate |
|---|---|---|
| Magnification and field of view | Magnification = eyepiece × objective. Field of view = eyepiece field number ÷ objective magnification. | Exact according to the spec sheet. Some spec sheets describe the series: the specific set of objectives is still to be confirmed model by model. |
| Resolution | Rayleigh criterion: 0.61 · λ / N.A., with λ = 0.55 µm. | Theoretical value, with the condenser properly adjusted. |
| Useful magnification | Between 500 and 1000 times the numerical aperture. | Above that, the image gets bigger without showing more detail. |
| Shape of the red blood cell | Evans and Fung equation: total thickness h(ρ) = √(1−ρ²)·(C0 + C2ρ² + C4ρ⁴), with R0 = 3.91 µm, C0 = 0.81 µm, C2 = 7.83 µm and C4 = −4.39 µm. It gives a diameter of 7.82 µm and a maximum thickness of about 2.6 µm. | Size variation of ±4.5%, chosen by us (the usual range is 7.5–8.7 µm). |
| Brightfield | Light is attenuated according to thickness (Beer-Lambert): that is why the centre comes out paler. | Stain colour chosen by eye, leaning towards Giemsa pink. |
| Phase contrast | Brightness according to the phase shift: refractive index of the red blood cell ≈ 1.40 versus ≈ 1.35 for plasma. | Halo and intensity: qualitative approximation. |
| Darkfield | Edges and slopes, which scatter the light, shine. It is a common technique for observing blood: Euromex presents its darkfield iScope as ideal for live blood analysis. | Approximate intensity. The instruments in the shop with darkfield as standard do it at 1000×. |
| Polarisation | Only birefringent material shines; the stage rotates. | The red blood cell is only very slightly birefringent (about 3.5 nm of retardance): with a classroom microscope it cannot be seen. |
| Proportions | One platelet for every ~33 red blood cells (5.4 million versus ~160,000 per µL). Neutrophil of 11 µm with 4 lobes. | The neutrophil is deliberately placed near the centre; in normal blood there is roughly one white blood cell for every 500–1000 red ones. |
Sources
- Spec sheets of the Letscopes microscopes.
- Evans E, Fung YC. Improved measurements of the erythrocyte geometry. Microvascular Research 1972;4(4):335-347. PubMed 4635577.
- Equation parameters, as reproduced in Pozrikidis and Dimitrakopoulos, Biophysical Journal 2010 (PDF).
- Sizes, counts and colours of blood cells: Anatomy & Physiology II (Lumen) and Erythrocytes (Lumen).
- Refractive index: Frontiers in Photonics 2025. Birefringence: PubMed 25396712.
- Darkfield as standard (cardioid condenser and S100× oil objective with iris, 1000×): Euromex, iScope darkfield and bScope darkfield.
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