Optics Overview

This section makes the connection between one lens and the four-lens system we are employing in our microscope.

In the next few series of images, the green lines are light, the dark vertical lines are lenses, the dots on the x-axis are one focal length away from the nearest lens, the red dashed lines are images, and the thick red line at x = 0 is the object being observed.

Single Lens

Look at the following images and observe how the image formed is a real image that gets larger as the object approaches the focal length.

The image reaches a maximum size when the object is just outside of the focal length.

As the object passes the focal length, the image becomes a large virtual image.

The virtual image gets smaller as the object continues to move closer to the lens.

Compound Microscope

Now to make a compound microscope, start with an object just outside of the focal length of a lens so that a larger real image is formed.

Add a second lens, with the image from the first lens just inside the second lens' focal length.

Because the image from the first lens is a real image, it can act as the object for the second lens. The second lens will create a large virtual image because the 'object' is inside its focal length.

To provide a sense of scale, the y-axis has been compressed to show the size of the final image. This compound microscope has about 22x magnification.