The first microscope had a simple single-lens design. Single-lens microscopes could be considered complicated magnifying glasses. Like a magnifying glass, a single-lens microscope can only magnify an object to one degree, regardless of adjustments. A compound lens microscope, however, contains more than one lens. The combination of lenses available in this type of microscope means that a user can change levels of magnification and can magnify an object up to 2,000 times its size.
There are two basic types of lenses in a compound microscope. These two types of lenses are called ocular lenses and objective lenses. The ocular lens is the lens situated in the eyepiece. This is the lens the user looks through to see the object on the slide. Compound microscopes can be either monocular or binocular, depending on the number of eyepieces. A monocular compound microscope has one eyepiece, while a binocular scope has two eyepieces, allowing for a three-dimensional view. According to the State University of New York, the typical magnification of the ocular lens is 10X.
The objective lens is the lens closest to the object on the slide. Compound microscopes differ in the number of objective lenses available for magnification. Some microscopes have three objective lenses, while others have four to provide greater magnification strength. Objective lenses can have magnification levels of 4X, 10X, 43X, 93X and 100X. The objective lens and ocular lens work together to create a detailed, magnified image of an object.
The number posted on the objective lens determines the amount of magnification seen through a 10X ocular lens. For example, a 10X objective lens combined with a 10X ocular lens produces a 100X magnification, and a 40X objective lens combined with a 10X ocular lens produces a 400X magnification. Users must adjust the focus of the lenses each time they switch magnification.