Key Precautions for Using Optical Microscope
As a commonly used instrument in high school biology experiments, the correct use of microscopes directly affects the success or failure of many biological experiments. Pointing out some errors in students' use of microscopes and guiding them to use microscopes correctly should be an extremely important part of middle school biology experimental teaching. In the practice of biology teaching, the author believes that it is necessary for teachers to emphasize the following points during lectures, based on the observation of students' use of microscopes and some problems reflected in their experimental tests.
1, The issue of correct installation
Before using a microscope, first install the eyepiece and objective lens of the microscope. The installation of the eyepiece is relatively simple, but the main problem lies in the installation of the objective lens. Due to the high value of the objective lens, if the thread is not properly closed during installation, it is easy for students to fall to the ground and cause damage to the lens. Therefore, for safety reasons, it is emphasized that students should use their left index and middle fingers to hold the objective lens when installing it, and then use their right hand to install it. This way, even if it is not installed properly, it will not fall to the ground.
2, Correctly addressing the issue of light
Focusing on light is an important step when using a microscope. Some students randomly rotate an objective lens towards the light hole instead of using a low magnification mirror as required. I like to use one hand to turn the mirror, often causing it to be pulled down. So when guiding students, teachers must emphasize the use of low magnification mirrors for light. When the light is strong, small aperture and flat mirrors are used, while when the light is weak, large aperture and concave mirrors are used. Reflective mirrors should be rotated with both hands until a uniform and bright circular field of view is seen. After aligning the light, do not move the microscope casually to prevent the light
from accurately entering the through hole through the reflector.
3, The problem of using the accurate focus spiral correctly
Using a quasi focus spiral to adjust the focal length and find the object can be said to be the most important step in microscope use, and it is also a difficult step for students to find. Students are prone to the following errors during the operation process: firstly, focusing directly under high magnification; Secondly, regardless of whether the lens barrel rises or falls, the eyes are always looking into the field of view through the telescope; Thirdly, there is a lack of understanding of the critical value of object distance. When the object distance is adjusted to 2-3 centimeters, it is still increasing upwards, and the speed of rotating the quasi focus spiral is very fast. The first two types of errors often cause the objective lens to collide with the mounting, damaging the mounting or lens, while the third type of error is a common phenomenon among students when using microscopes. In response to the above errors, teachers must emphasize to students that adjusting the focal length must be done by lowering the low-power lens. First, rotate the coarse focus screw to slowly lower the lens barrel and bring the objective lens closer to the glass slide. However, be careful not to let the objective lens touch the glass slide. During this process, the eyes should look at the mirror from the side, then use the left eye to gaze into the eyepiece, and slowly adjust the coarse focus screw in reverse to slowly raise the lens barrel until the object image is seen. At the same time, explain to students that the object distance of a microscope is usually around 1 centimeter.
Therefore, if the object distance has exceeded 1 centimeter but the object image is still not seen, it may be that the specimen is not in the field of view or the coarse focus screw rotation speed is too fast. At this time, adjust the mounting position and repeat the above steps. When a blurry object image appears in the field of view, it is necessary to switch to fine focus spiral adjustment. Only in this way can, In order to narrow down the search range and improve the speed of finding objects.
