Correct use of quasi-focus helix in optical microscope
Using the quasi-focus screw to adjust the focal length and finding the object image can be said to be the most important step in the use of the microscope, and it is also the most difficult step for students. Students are prone to the following mistakes in operation: one is to directly adjust the focus under a high-magnification lens; When it reaches 2 to 3 cm, it is still adjusted upwards, and the speed of turning the quasi-focus screw is very fast. The first two kinds of error results often cause the objective lens to interfere with the mounting film and damage the mounting film or lens, while the third error is the most common phenomenon when students use the microscope. In response to the above mistakes, the teacher must emphasize to the students that the adjustment of the focal length must be done at a lower magnification, first turn the coarse and accurate focus screw, so that the lens barrel slowly descends, and the objective lens is close to the slide glass, but be careful not to let the objective lens touch the slide glass In this process, the eyes should look at the objective lens from the side, and then stare into the eyepiece with the left eye, and slowly adjust the coarse quasi-focus screw in reverse, so that the lens barrel slowly rises until the object image is seen, and at the same time point to the students It shows that the object distance of a general microscope is about 1 cm, so if the object distance is far beyond 1 cm, but the object image is still not seen, it may be that the specimen is not in the field of view or the coarse and accurate focus helix is turned too fast, and you should adjust it at this time. Install the film position, and then repeat the above steps. When blurred objects appear in the field of vision, it is necessary to switch to the fine focus screw adjustment. Only in this way can the search range be narrowed and the speed of finding objects can be increased.
