Microscopy guide: choosing a laboratory microscope, objectives and slides
Choose a microscope by the sample and the contrast method first, then by the objectives. The numerical aperture (NA) of the objective, not the total magnification, sets how much detail you can resolve.
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Last updated: 24 October 2026
Which microscope fits which task?
| Microscope | Image | Typical use |
|---|---|---|
| Upright compound (brightfield) | Transmitted light, 40× to 1000× | Stained smears, histology, haematology, teaching |
| Stereo microscope | 3D view, about 5× to 80× | Dissection, sorting, inspection, colony counting |
| Inverted microscope | Objectives below the stage | Cell culture in flasks and plates |
| Phase contrast | Contrast without staining | Living cells, sperm, urine sediment |
| Fluorescence | Filter sets for specific dyes | Immunofluorescence, FISH, reporter proteins |
| Digital microscope or camera | Image on screen | Documentation, teaching, telepathology |
Typical values for guidance; always check the manufacturer's data sheet. Sources: see Official sources below.
Reading an objective
An objective engraved 40×/0.65 ∞/0.17 magnifies 40 times, has an NA of 0.65, is corrected for an infinity optical path and for a 0.17 mm cover glass. The resolution limit is roughly d ≈ 0.61 λ / NA: with green light (550 nm) and NA 1.25 oil immersion you reach about 0.27 µm. Achromat objectives suit routine work, plan achromats give a flat field for imaging, and apochromats offer the best colour correction for fluorescence and publication images. Use immersion oil only with objectives marked Oil.
Slides, cover glasses and daily care
- Standard slides measure 76 × 26 mm; frosted or coloured ends make labelling easier, adhesive slides keep tissue sections in place.
- Most objectives expect cover glass thickness no. 1.5 (0.17 mm).
- Set up Köhler illumination at the start of each session for even light and the best contrast.
- Clean lenses with lens tissue and a suitable lens cleaner, never with ordinary paper; remove oil immediately after use.
- A microscope used for diagnosis in a clinical laboratory may fall under the IVDR; check the manufacturer's intended purpose.
Frequently asked questions
Is higher magnification always better?
No. Above about 1000 times the NA, magnification is empty: the image gets larger but not sharper. Choose objectives with a higher NA for more detail.
Which cover glass thickness should I use?
Most objectives are corrected for 0.17 mm, which is thickness no. 1.5. A thicker or thinner cover glass reduces contrast and sharpness, especially with high-NA dry objectives.
Can I add a camera to an existing microscope?
Usually yes, through a trinocular port or an eyepiece adapter with the right C-mount reduction. Check the sensor size and the adapter factor so the image is not cropped.
Upright or inverted microscope for cell culture?
Inverted. The objectives sit below the stage, so you can observe living cells through the bottom of flasks, dishes and plates. Upright microscopes are designed for slides.
LED or halogen illumination?
LED is the default today: long life, little heat and a constant colour temperature at every brightness. Halogen remains on older and some specialised instruments.
Brightfield, phase contrast or fluorescence?
Brightfield for stained samples such as smears and tissue sections. Phase contrast for unstained living cells. Fluorescence for targets labelled with dyes or antibodies; it needs a suitable light source and filter sets.
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