How Real is the Image Formed By a Light Microscope?

Microscopes form enlarged images of microscopic objects.

In optics, images are called real if the light actually comes from where the image appears to be. A virtual image, by contrast, forms when light appears to come from the image location but really comes from elsewhere.

Types

Flat mirrors are a common example of a virtual image. When you look into a mirror, you see an image of yourself that appears to be standing somewhere behind the mirror. Since the light in this case is not actually coming from where the image appears to be, this kind of image is virtual. The lens in a movie projector, by contrast, forms a real image on the screen.

Function

In a compound light microscope, the objective lens refracts or bends the light from the specimen to create a slightly enlarged real image between the objective and the eyepiece. The eyepiece lens then refracts the light to create a virtual image of the real image formed by the objective lens. The image you see through a microscope is thus a virtual image of a real image.

Effects

This virtual image is greatly enlarged compared to the original specimen and appears to be farther away than the specimen really is. The ratio between the angle subtended by the object and the angle subtended by the virtual image is called the magnification.

References

• "Physics for Scientists and Engineers"; Richard Wolfson and Jay Pasachoff; 1999.
• Olympus Microscopy Center: The Concept of Magnification