Oil Immersion

This is the setup for oil immersion the Olympus CH30 microscope.

The numerical aperture of a lens is dependant on the angle of acceptance and the index of refraction of the medium (n). Most lenses are design to be use air as the medium, which has an index of refraction of1.0. "Oil lenses" are designed to have immersion oil placed between the specimen and the lens. Most immersion oils have a refractive index of 1.4 or better. This allows for a larger numerical aperture and ultimately better resolution. However, they are more cumbersome to use and have limitations on the type of specimen. A lens that is to be used with oil will have the word "oil" on the barrel. These types of lenses will not work without the oil.

1. Use a specimen that is dry or has a sealed cover glass on it. Set up the microscope for Kohler illumination. Using the "High dry" (40X) objective, locate and focus the area of interest on your specimen.

2. Rotate the objective turret so it is between the high dry and oil objectives.

3. Place a drop of immersion oil on the top surface of the slide.

4. Rotate the oil objective into position with the objective turret.

5. Focus the image using the fine focus knob only.

6 Adjust the iris diaphragm for best resolution. (N.A. ~ 1.0)

After using an oil immersion lens clean up the microscope stage, slide and the objective lens. On the lens, be sure to use only soft lens paper (Kodak Lens Paper). Do not use Kimwipes. The oil is messy and is the largest source of optical contamination for the other objectives.