A microscope may be a combination of:

A compound microscope consists of two convex lenses: an objective lens (with a short focal length) placed near the specimen, and an eyepiece (with a relatively longer focal length) through which the observer views the magnified image. The objective forms a real, inverted, magnified image which serves as the object for the eyepiece, which then acts as a simple magnifier to produce a final virtual and highly magnified image. Therefore, a microscope is typically a combination of two convex lenses.