What is an immersion objective, and when is it used?

The 100x oil immersion objective lens one of the most powerful tool in a light microscope, essential for preserving image clarity, brilliance, and resolving power by minimizing the detrimental effects of refractive index differences, such as when light passes from air to glass. Immersion oil, matching glass's refractive index, eradicates refraction at the glass-oil interface. To effectively use this lens, first focus meticulously on the stained specimen with the 40x objective, keeping the focus steady. Then, half-rotate the turret to align both the 40x and 100x objectives around the specimen, place a small drop of immersion oil directly on the slide to cover the specimen, and finally, rotate the 100x objective into the specimen. Adhering to three vital rules is essential: always use the oil immersion lens with oil, prevent oil from contacting other lenses, and thoroughly clean up any residual oil after use.