How to use a biological microscope

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1) Preparation: When picking up the microscope, one must hold the arm firmly with the right hand and support the base with the left hand; it is not allowed to pick it up with just one hand. Before placing the microscope on the left shoulder, keep the base about 5 cm away from the edge of the lab table. Then check whether the lighting source is appropriate. 2) Turn the rotator toward the light so that the low-power lens is aligned with the light aperture and about 2 cm above the stage. Then, use either the left eye (for single-lens microscopes) or both eyes (for binocular microscopes) to look through the eyepiece, adjusting the size of the diaphragm on the base until the entire field of view appears bright and even to the left eye or both eyes. The size of the aperture or the elevation of the condenser can also be adjusted to control the intensity of the light. Use the appropriate filter if necessary. Generally, observing colorless parenchyma cells, the layers of starch grains, and tiny calcium oxalate crystals requires darker light. Thicker tissues, as well as colored thick-walled cells, require stronger light. 3) Specimen slide: After illuminating it, clamp the specimen slide to be observed on the mover of the stage so that the area to be viewed is placed under the objective lens. 4) Selection of the objective lens: The choice of objective lens depends on the size of the object to be observed. Use a low-power lens of 10x, or a high-power lens of 40x; if necessary, use a 100x oil immersion lens. 5) Selection of the eyepiece: The selection of the eyepiece must be coordinated with that of the objective lens in order to achieve a reasonable magnification level. If the eyepiece is not chosen appropriately, the image may become unclear or difficult to view. For example, when using an 40x objective lens, a reasonable magnification is 600 times; therefore, it is best for the eyepiece’s magnification to be no more than 15 times (i.e., 40x15=600). 6) Focal length adjustment: (1) When using a microscope for observation, it is important to follow a specific order: start with a lower magnification level first, then move to a higher one; use coarse adjustment first, and then fine adjustment. During operation, the objective lens should be lowered slowly, bringing the rotary evaporator as close as possible to the cover glass (be careful to avoid collision between the lens and the cover glass, which could damage the lens), and then raised step by step while keeping an eye out for the target. It is advisable to first conduct a comprehensive observation using a low-power microscope; turn the coarse adjuster until the image in the field of view is visible, and then adjust the fine adjuster until the image becomes clear. If a more detailed examination of a specific area is desired, that area must first be moved to the center of the field of view, after which a high-power microscope can be used for observation. At this point, the focal length needs to be adjusted again to achieve a clear image, but usually only a slight turn of the fine adjuster is required. (2) When using an oil immersion lens, first add 1 drop of cedar oil to the cover slip (the refractive index of cedar oil is 1.515, which is roughly equal to that of glass), so as to create a uniform refractive layer between the front lens of the objective lens and the cover slip, thereby increasing the amount of light. Adjust the focal length as above again. (3) Posture for microscopic observation. The microscope should be placed on a fixed laboratory table; the surface of the table should not be too high, so that it is not difficult to observe while sitting. In the case of a single-lens microscope, one generally uses the left eye to look through the lens while using the right eye to watch the stage, and simultaneously draws or records the observed image. The method of opening and closing the eyes repeatedly can easily cause eye fatigue, and it is important to correct this habit. During operation, use the left hand to turn the fine adjuster and the right hand to turn the mover on the stage, in order to locate the field of view and adjust it until the image is clear.