Microscopes are instruments that allow us to visualize objects too small to be seen with the naked eye. An important part of these devices is the objective lens system, which primarily magnifies the specimen. Objective lenses are intricate components, often consisting of multiple individual lenses, that achieve high-quality magnification. They are positioned closest to the sample, collecting light to form an initial magnified image.
Typical Number on a Standard Microscope
A standard compound light microscope features multiple objective lenses, usually three to four. These cylindrical lenses are threaded into a revolving nosepiece or turret. The nosepiece is located beneath the microscope’s head and above the stage. The objective lenses are arranged circularly on this nosepiece, allowing for easy selection. Each objective lens is distinct in size, with lower magnification lenses being shorter and higher magnification lenses longer.
The Purpose of Multiple Magnifications
Microscopes are equipped with multiple objective lenses to provide varying levels of magnification and resolution. This allows observation at different degrees of detail, from broad overviews to minute cellular structures. Common magnification powers include 4x, 10x, 40x, and 100x. The 4x objective, often called a scanning lens, offers the widest field of view, suitable for initially locating the specimen on the slide. The 10x lens, or low power objective, provides a general view.
The 40x objective, known as the high power objective, allows for more detailed examination of cellular features. For the highest detail, such as viewing individual bacteria or subcellular components, the 100x objective is used. This lens requires the application of immersion oil to enhance image clarity and resolution. The combined magnification of an objective lens and the eyepiece (ocular lens), which typically magnifies 10x, determines the total magnification.
Operating Objective Lenses
Operating objective lenses involves a systematic approach for clear viewing and to prevent damage. Switch between different objectives by gently rotating the revolving nosepiece until the desired lens clicks into place over the specimen. It is recommended to begin observation with the lowest power objective, such as the 4x lens. This allows for a wide field of view, making it easier to locate and center the specimen. Once the specimen is found and focused under low power, progressively rotate to higher magnification objectives.
As magnification increases, the working distance—the space between the objective lens and the slide—decreases. This requires careful manipulation of the focus knobs to avoid contact between the lens and the slide. The 100x objective lens, designed for oil immersion, requires a drop of immersion oil to be placed on the slide. This oil minimizes light refraction and maximizes light collection, resulting in a sharper and brighter image. After using immersion oil, clean the lens thoroughly with lens paper to prevent residue buildup.