Brief Analysis on How to Properly Use the Objective Lenses and Focusing of a Microscope
When using a microscope, follow the focusing principle: start with low power then switch to high power. Focusing under the low-power objective serves as preliminary focusing for the high-power objective. When switching to the high-power objective, simply rotate the objective lens into position (the focal distance preset with the low-power objective remains unchanged). Under high magnification, tissues can be observed with only slight focusing adjustment, or even no adjustment at all. However, many operation manuals omit the specific definition of the "low-power objective".
During microscope operation, the 10× objective lens is the standard and commonly used lens for focusing. The reason is that switching from the 10× objective to either lower or higher magnification objectives will not cause drastic changes. Another reason is that objectives with even lower magnification have a greater depth of field, making it difficult for users to focus accurately with the naked eye. Directly switching to a high-power objective afterwards may easily cause collision between the sample and the lens.
Meanwhile, the 10× objective is not only the standard lens for focusing but also widely applied in practical work. For example, many national standards for metallographic inspection commonly use standard reference atlases observed under 100× magnification. The 100× magnification is achieved by combining a 10× objective with a 10× eyepiece. From a practical operation perspective, if operated properly, the previous operation should bring the objective near the focal plane. After the sample is correctly positioned under the 10× objective, a blurry or relatively clear image will appear, which only requires fine focusing adjustment.
(2) About Parfocality Our experience regarding focusing after switching from low-power to high-power objectives differs greatly from descriptions in other documents. Thanks to improved microscope manufacturing technology, modern microscopes feature good parfocality among different objectives, especially imported models. After achieving sharp focus under low magnification, switching to high magnification may yield a clear image without refocusing; or only a tiny increase in working distance is needed. The adjustment is not measured by 1 to 3 rotations, but merely 1 to 3 degrees - an extremely minor adjustment.
(3) About the Objective Nosepiece Do not directly grip the objective lens by hand when changing objectives. Otherwise, the threads securing the objective may loosen and lead to tilted optical axis. The microscope objective and digital microscopic imaging system are fastened onto the objective nosepiece. When switching objectives, rotate the nosepiece until a soft "click" sound is heard and a noticeable resistance is felt. At this point, the objective is in its normal working position, perpendicular to the stage plane.
