The lens you look through on a compound light microscope is called the eyepiece, or ocular lens. Typically, the eyepiece is found at the top of the microscope and it is where the viewer looks to see the magnified image of the specimen being examined.
The eyepiece usually contains a lens that further magnifies the image produced by the objective lenses below it. Most eyepieces have a standard magnification of 10x or 15x, but there are variable eyepieces available that allow for different levels of magnification.
In essence, the eyepiece is crucial for viewing specimens because it not only helps magnify the image but also allows for comfortable observation. Some microscopes may also have additional features in the eyepiece, such as a pointer for locating specific areas within the field of view.