microscope objective lens function

Microscope Objective Lens Function

All parts of the microscope are important, but the objective lenses - the lower, magnifying lenses - must be treated with particular care. The lenses are of the best quality and need to be handled very carefully. Sometimes two lenses are glued together, and you must be careful not to use solvents such as strong alcohol solutions or acetone, which could dissolve the glue or cement.

Objectives are referred to by their magnifying power, which is marked on the side. The microscope you will use has the following objectives:


• x 10
• x 40
• x 100 (this objective is often called the oil immersion objective; sometimes it has a black or red ring around it for easy identification).

Objectives, showing working distance between front lens and specimen

The mechanical stage

The mechanical stage holds the slide secure and allows the specimen to be moved smoothly backwards, forwards or sideways. Sometimes a scale is fitted to two sides of the stage to show the extent of the movement. This is called the Vernier scale, and it is useful to know how to use it; it can be used to trace a part of the blood film that you need to re-examine or show to your supervisor.

Substage condenser (with iris diaphragm)

The substage condenser is made up of a number of lenses. These centre the light from the mirror, or electric light source, to a central spot on the field. The substage condenser can be raised or lowered to give maximum or minimum illumination.

Inside the condenser is the iris diaphragm. This is used to control the amount of light passing through the condenser. The iris diaphragm consists of a number of interlocking leaves made of a thin metal. It is adjusted by means of a lever.

Filter holder and blue filter

Beneath the iris diaphragm is the filter holder. This is where a blue filter is placed when you use an electric light source for illumination. It has the effect of making the microscope field white rather than yellow.