Compound Microscope

A compound microscope consists of two convex lenses co-axially separated by some distance. The lens nearer to the object is called the objective. The lens through which the final image is viewed is called the eyepiece.

Angular Magnificationor Magnifying Power of the Compound Microscope

Angular magnification or magnifying power of a compound microscope is defined as the ratio of the angleβsubtended by the final image at the eye to the angleαsubtended by the object seen directly, when both are placed at the least distance of distinct vision.

∴Angular magnification,

Since the angles are small,

α ≈tanα

β≈tanβ

Thus, the magnification produced by the compound microscope is the product of the magnifications produced by the eyepiece and objective.

Where,M_{e}andM_{0}are the magnifying powers of the eyepiece and objective respectively

The linear magnification of the real inverted image produced by the eyepiece is.

Linear magnification,

Where,

→Focal length of the eye piece

is the linear magnification of the object produced by the objective.

From (i), (ii), and (iii),

We know that,

Magnifying power, when final image is at infinity:

Ifu_{0}is the distance of the object from the objective andv_{0}is the distance of the image from the objective, then the magnifying power of the objective is

When the final image is at infinity,

Magnifying power of compound microscope,

If the object is very close to the principal focus of the objective and the image formed by the objective is very close to the eyepiece, then

Where,

L= Length of the microscope

In this case, the microscope is said to be in normal adjustment.