Why Is Oil Immersion Used With Microscopes?

Some of the implements used in microscopy can be unintuitive.

Oil immersion is used with high-powered settings on light microscopes in order to avoid the loss of clarity associated with refraction. By having roughly the same index of refraction as glass, immersion oil enables viewing of slides with minimal refraction.

Considerations

High-powered objectives on microscopes are often designed especially for use with oil immersion techniques; these will not function properly without oil, and can even be broken if such is attempted. Similarly, objectives designed for dry use are not compatible with oil immersion techniques, as the scope is too short.

Significance

Oil immersion makes microscopy a far more powerful tool than it would otherwise be, by enabling clear imaging in microscopes at much higher magnifications than allowed by "dry" viewing. This also makes the refraction index of the oil quite significant; while most immersion oils available are standardized, it is possible to get oils with different indexes. Using oils with different indexes will complicate readings.

Effects

Oil immersion is only compatible with fixed slides: living microbes on a slide will not stay alive very long if they find their environment saturated with synthetic oil. Immersion oil also certainly has effects on the view, such as absorbing certain portions of the optical spectrum, so it takes training to adjust the eye.

References

• Cargille Labs: Immersion Oil and the Microscope
• UC - Clermont College Biology: Immersion Oil Microscopy