A compound microscope is an optical instrument designed to magnify minute objects for detailed observation. It achieves this magnification through a system involving two or more lenses, specifically an objective lens and an eyepiece. This dual-lens setup reveals intricate structures otherwise invisible to the unaided eye.
Microscopes play an important role in various scientific and educational fields. In scientific research, they examine cellular structures, tissues, and microorganisms, aiding discoveries in biology and medical diagnostics. In education, microscopes provide hands-on experience, enhancing understanding of microscopic life and biological principles.
Familiarizing Yourself with the Microscope
Before operating a compound microscope, understanding its key components and their functions is important. The microscope’s stability comes from its base, which rests on the work surface, and the arm, which connects the head to the base and provides a handle for transport. The head houses the optical components, including the eyepiece, through which a user looks, often providing 10x or 15x magnification.
Below the eyepiece, the revolving nosepiece holds multiple objective lenses, ranging from 4x to 100x power. The stage is the flat platform where microscope slides are placed for viewing, often equipped with stage clips to hold the slide securely. Beneath the stage, the illuminator provides light that passes through the specimen.
The diaphragm, located beneath the stage, controls the light’s intensity and contrast, adjusting the amount of light reaching the specimen. Two adjustment knobs are present for focusing: the coarse adjustment knob for large stage movements, and the fine adjustment knob for smaller, precise adjustments.
Setting Up and Viewing Your Specimen
To begin observing a specimen, place the microscope on a stable, level surface, plug it in, and turn on the illuminator. Preparing a specimen involves placing it on a glass slide and covering it with a coverslip. For liquid samples, a small drop is placed on the slide, and a coverslip is gently lowered at an angle to avoid air bubbles.
Next, rotate the revolving nosepiece to position the lowest power objective lens directly over the stage aperture. Place the prepared slide onto the stage, securing it with the stage clips, and center the specimen over the light source. While looking from the side, use the coarse adjustment knob to bring the objective lens as close to the coverslip as possible without touching it.
Then, look through the eyepiece and slowly turn the coarse adjustment knob to move the stage downwards until the specimen comes into approximate focus. The coarse adjustment knob should only be used with the lowest power objective lens to prevent accidental contact between the lens and the slide. Once a rough focus is achieved, use the fine adjustment knob to sharpen the image.
Optimizing Your View
Once the specimen is in focus under the lowest power, refining the view involves adjusting light and magnification. The diaphragm beneath the stage controls the amount of light reaching the specimen, impacting image brightness and contrast. Adjusting this lever enhances clarity, as too much light can wash out details.
To increase magnification, rotate the revolving nosepiece to switch to a higher power objective lens. At higher magnifications, the working distance between the objective lens and the slide is reduced. Therefore, only the fine adjustment knob should be used for focusing when observing with medium or high power objective lenses to prevent damage to the lens or the slide.
For the highest magnifications, certain objective lenses require the use of immersion oil. This oil is applied directly to the coverslip, filling the air gap between the lens and the slide. Immersion oil has a refractive index similar to glass, which minimizes the bending and scattering of light rays as they pass from the slide into the objective lens, improving resolution and clarity at high magnifications.
Microscope Care and Maintenance
Proper handling and maintenance are important for the longevity and performance of a compound microscope. Always carry the microscope with two hands, supporting the arm with one hand and the base with the other, to prevent damage. When not in use, protect the microscope from dust and debris by covering it with a dust cover.
Careful cleaning of the lenses is required to avoid scratches and damage. Use specialized lens paper or cotton swabs moistened with appropriate lens cleaning solution, wiping gently in a circular motion from the center outwards. Avoid using regular tissues, clothes, or harsh chemicals like acetone on lenses, as these can leave scratches or dissolve plastic components.
After using oil immersion lenses, clean off the oil immediately with lens paper and an oil-soluble solvent to prevent residue buildup. When finished, lower the stage, rotate the lowest power objective lens into position, and remove the slide. Store the microscope in a cool, dry place, away from corrosive chemical fumes, and ensure the power is switched off and the illuminator has cooled down before storage.