Multiple Lens Deals:  Many instruments that use lenses use several of them in series - telescopes, microscopes, camera lenses, film projectors, etc.  The way this works is that the first lens forms an image of an object.  This image serves as the object for the next lens and so on.

Here is a typical simple set up, two lenses and one object.

First we find the image formed by the first lens.

The first image will then act as an object to the second lens, which will form a final image.