If the distance between lenses is negligible, the lenses are said to be in contact. The power of this combination of lenses is additive:
where is the power of the multiple lenses and f is the focal length of the multiple lenses.
Lenses separated by a distance that is not negligible are treated separately. Light passes through the first lens, forming an image. This image serves as the object for the second lens. Light from this image passes through the second lens, creating a final image from the combination of lenses. In this case, the magnification of the system is the product of the magnifications of the image through each of the lenses.
