Light & Color

Image Relay

Four large converging lenses are spaced two focal lengths apart. Two visitors sit at opposite ends of this chain of lenses. They sit two focal lengths from the end lenses. Each visitor sees the image of the other relayed by the chain of lenses. Each image appears bright, life-size, and right-side-up. Each lens can be rotated out of the chain of lenses to show the role it plays in the formation of the image.
This exhibit illustrates how lenses form real images. It also shows the role of field lenses in image formation.
The lens nearest one visitor can be slid back and forth to see how this influences the final image.
A set of three lights can be flipped into place replacing one of the visitors—this requires a key. In addition, there is a locked box available to teachers which contains:
1. viewing screens which are used to search for real images
2. a small circular aperture to show the effect of stopping down a lens on spherical and chromatic aberration.
3. a thin circular arc aperture to contrast with the circular aperture.
The pattern of lenses, that is how many and which ones are placed in the image-forming path, affect the appearance of the image.