Motic BA210E, Instruction Manual

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6. USING OIL IMMERSION OBJECTIVES

Oil immersion objectives are labelled with the additional engraving “Oil” and are to be immersed in
oil between the specimen and the front of the objective.

The immersion oil supplied by Motic is synthetic, non-fluorescing and non-resining oil, with a
refractive index of 1.515

Normally, cover glass must be used with oil immersion objectives with a few exceptions.
Deviations from thickness are not important as a layer of immersion oil acts as compensation above
the cover glass.

The small bottle of oil supplied with every immersion objective facilitates application of the oil to the
cover slip.

Remove any air bubbles in the nozzle of the oil container before use.

Immersion oil must be used sparingly. After the examination, the oil should be wiped off the
objective with a lens cleaning tissue and the residual film removed with soft cloth moistened with
petroleum benzene or absolute alcohol.

Locate the field of interest with a lower magnification objective. Swing the objective out of the light
path, and add one drop of immersion oil over the site of the specimen.
Swing in the oil immersion objective. There should be a small column of oil from the cover slip to
the objective lens. Use the fine focus to make the image sharp.

Freedom from air bubbles must be ensured. To check for air bubbles, remove an eyepiece, fully
open the field and aperture diaphragms, and look at the exit pupil of the objective within the
eyepiece tube. Air bubbles are recognized by presence of a surrounding black ring. Bubbles may
often be dislodged by moving the slide to and fro or by slightly rocking the revolving nosepiece back
and forth. If not successful in clearing the bubbles then the oil must be wiped off and replaced with
a fresh drop.