Problems with the correct use of quasi-focal spirals in optical microscopes
Using the focus screw to adjust the focus and find the object image can be said to be the most important step in using a microscope, and it is also the step that students find most difficult. Students are prone to make the following mistakes during operation: First, they adjust the focus directly under high-power lenses; Second, their eyes always look at the field of view in the eyepiece regardless of whether the lens barrel rises or falls; Third, they do not understand the critical value of the object distance and adjust the object distance. When it reaches 2 to 3 centimeters, it is still adjusting upward, and the speed of turning the focus screw is very fast. The first two errors often result in the objective lens colliding with the mounting film and damaging the mounting film or lens, while the third error is the most common phenomenon when students use microscopes. In response to the above errors, teachers must emphasize to students that when adjusting the focal length, the focus must be adjusted at low magnification. First, turn the coarse focus screw to slowly lower the lens barrel. The objective lens is close to the glass slide, but be careful not to let the objective lens touch the glass slide. During this process, the eyes should look at the objective lens from the side, then look into the eyepiece with the left eye, and slowly adjust the coarse focus screw in the reverse direction, so that the lens barrel slowly rises until the object image is seen, and at the same time, the student Note that the object distance of a general microscope is about 1 cm, so if the object distance is far more than 1 cm but you still cannot see the object image, it may be that the specimen is not within the field of view or the coarse focus screw is turned too fast, and you should adjust it at this time Set the film loading position, and then repeat the above steps. When a blurry object appears in the field of view, you must switch to the fine focus screw adjustment. Only in this way can you narrow the search range and increase the speed of finding the object.
