The Celestron 400x Laboratory Biological Microscope is an all-metal bodied microscope with fully coated glass optics and advanced features usually offered on only higher priced microscopes, like a basic condenser and 5-position disc diaphragm. With both coarse and fine focus knobs, 3 objective lenses, an adjustable head (0 to 60), and 5 specimen slides, it's a great entry-level microscope that will last for years. A condenser concentrates and focuses light when using high-power objective lenses. Since these lenses tend to have very small apertures, a condenser combined with an iris diaphragm provides increased illumination and resolution. You can easily adjust brightness, contrast, depth of field, and evenness of illumination on your specimen.