Oil immersion
（重定向自Oil immersion lens）
![Principle of immersion microscopy. Path of rays with immersion medium (yellow) (left half) and without (right half). Rays (black) coming from the object (red) at a certain angle and going through the coverslip (orange, as the slide at the bottom) can enter the objective (dark blue) only when immersion is used. Otherwise, the refraction at the coverslip - air interface causes the ray to miss the objective and its information is lost.](/Images/godic/202501/30/Immersionsvorteil.svg5424.png")
![Two Leica oil immersion objective lenses. Oil immersion objective lenses look superficially identical to non-oil immersion lenses.](/Images/godic/202501/30/Leica_EpifluorescenceMicroscope_ObjectiveLens5424.jpg")
![Oil-immersion objective in use](/Images/godic/202501/30/Immersion_microscopy5425.jpg")
In light microscopy, oil immersion is a technique used to increase the resolving power of a microscope. This is achieved by immersing both the objective lens and the specimen in a transparent oil of high refractive index, thereby increasing the numerical aperture of the objective lens.