Most of the microscopes used today are compound. A compound microscope features two or more lenses. A hollow cylinder called the tube connects the two lenses.
The top lens, the one people look through, is called the eyepiece. The bottom lens is known as the objective lens. Below the two lenses is the stage, with the illuminator below that.
Compound microscopes were among the first magnifying instruments invented. Two Dutch eyeglass makers named Zaccharias and Hans Janssen are credited with making the first compound microscope in 1590 by putting one lens at the top of a tube and another at the bottom of the tube. Their idea was fleshed out by others scientists over the next several centuries, but the basic design remained very similar.
The eyepiece, also known as the ocular lens, is at the top of the compound microscope. It is not adjustable, that is, it only has one strength. Most ocular lenses are 10x, meaning that they magnify objects to ten times their normal size. People look in through the eyepiece through the tube and out through the objective lens.
A compound microscope normally contains several objective lenses. The objective lenses are different lengths, with the longer ones being the strongest. The lenses are situated on a round disk below the tube. Viewers choose which strength lens they want and place it below the tube by turning the disk until the desired lens is in place.
The stage and illuminator are below the objective lens. Specimens are placed over a translucent part of the stage. Light provided by the illuminator shines through the clear part of the stage, making it easier for the viewer to see the magnified details of the specimen. Two adjustment knobs help focus the object on the stage by bringing the lenses and the stage closer together.
Compound microscopes have been around for hundreds of years and are still very useful. A number of scientific disciplines use compound microscopes to discover the wonders of the microscopic world.