Why Do Compound Microscopes Invert the Images?

What is a Compound Microscope?

A compound microscope consists of both an eyepiece and an objective lens 1. In many compound microscopes, different objective lenses can be rotated into place, allowing for different magnification strengths. Both the eyepiece and the objective lens are converging lenses, which means that parallel light rays entering into the lens will converge to a single point (called the focal point).

How Does the Compound Microscope Invert an Image?

The objective lens in a compound microscope has a very short focal length 1. After the light passes through the specimen, past the objective lens, and past the focal point of the objective lens, the image formed will be inverted. This image is the object that is seen by the eyepiece lens. The eyepiece lens acts only as a simple magnifier, and enlarges the image created by the objective lens. As a result, the image that is seen when looking through a compound microscope is inverted when compared to the specimen being examined 1.

Implications of an Inverted Image

The inversion of an image under a compound microscope can be demonstrated by looking at the printed version of the letter "e" under the microscope 1. The image will be inverted due to the objective lens being convex. It can also be seen with larger specimens where the orientation is known (for example, if the head of an insect is directed towards the top of the slide.)