Final answer:
Always start and end with the lowest power objective lens, usually the 4x or 10x, when using a microscope due to their parfocal nature. This approach ensures initial focusing is easier and the specimen is protected when increasing magnification and when storing the microscope.
Step-by-step explanation:
Proper Microscope Handling and Usage
For safe and effective use of a microscope, there is a specific objective lens that should always be in place when starting to view a specimen, when first identifying objectives during use, and when storing the microscope. This lens is the lowest power objective, commonly the 4x or 10x lens. Begin with this objective to set the working distance and use the coarse focus knob to obtain a general focus. This is crucial because microscopes are parfocal, meaning once something is focused under a low power objective, it requires only minor adjustments with the fine focus knob when switching to higher power objectives. When finished, always return to the low power objective before putting the microscope away to prevent damage to the slides or lenses and to respect the working distances, particularly as higher magnifications have shorter working distances, which can lead to collisions with the stage.
Furthermore, proper illumination adjustments are necessary as magnification increases, since the lens aperture decreases in size. Always handle the microscope with care, carrying it with two hands and without sliding it on the bench, and return the microscope with the ocular lenses facing in when storing.