Page 25 - MNUmicrobiology practical 2025

General Microbiology & Immunology (PM 401) second level Semester 4 2024/2025

• An oil immersion lens helps to remedy this problem by eliminating the air gap

between the specimen and the objective lens.

• A drop of special immersion oil is placed on the microscope slide, and the oil

immersion objective lens is maneuvered so that it is touching the oil.

• Immersion oil has the same refractive index as glass so that the light passes

through the slide, specimen, oil and objective lens as if they were a single piece of

glass

Hint

In order to overcome the difference of refractive index between glass

(n=1.52) and air (n=1); cedar wood oil (n=1.52) is used.

Magnification power

The objective lens system produces an image of the specimen, which is then further

magnified by the ocular lens (eyepiece). The magnification of this lens is engraved on

the ocular. The total magnification of the microscope is determined by the combination

of the magnification of the objective lens and ocular lens that is in use, that is:

Total magnification = objective lens X ocular lens (eyepiece)

General Microbiology & Immunology (PM 401) Practical note Page 14