Precautions for Operation of Optical Microscopes
1. Proper Installation
Before using an optical microscope, the eyepiece and objective lenses must first be installed. Installing the eyepiece is relatively simple. The main risk lies with the objective lens. Objective lenses are expensive. If the thread is not properly engaged during installation by students, the lens may fall to the ground and get damaged. For safety, students are instructed to support the objective lens with the index and middle fingers of the left hand while screwing it in with the right hand. This prevents the lens from dropping even if the fitting is incorrect.
2. Correct Illumination Alignment
Light alignment is a critical step for microscope operation. Some students randomly align an objective with the aperture instead of starting with the low‑power objective as required. When adjusting the mirror, some use only one hand, which may pull the mirror loose. Teachers should emphasize the following: always use the low‑power objective for alignment. Use a small diaphragm and plane mirror for bright light conditions; use a large diaphragm and concave mirror for dim light. Adjust the mirror with both hands until an evenly lit circular field of view appears. Do not move the microscope after alignment, otherwise light may fail to enter the aperture correctly.
3. Proper Use of Focusing Knobs
Adjusting focus with the focusing knobs to locate the specimen image is one of the most important and difficult steps for students. Common operating mistakes include: ① Focusing directly under high magnification; ② Keeping eyes at the eyepiece while the barrel moves up or down; ③ Ignoring the critical working distance, continuing to raise the barrel rapidly when the distance reaches 2–3 cm.
The first two mistakes often cause the objective lens to collide with the slide, damaging both the slide and lens. The third error is frequently seen among student operators.
