Question

3. Which focus knobs can be used at each objective lens power?

Answer 1

There are two types of focusing knobs on a compound light microscope.

1. Coarse adjustment knob

2. Fine adjustment knob

The fine adjustment knob can be used at each objective lens power.

The coarse adjustment knob is used to adjust the distance between the specimen on the slide and the objective lens. Coarse adjustment knob should be used only with low power objective (e.g 10X) to bring the specimen in focus.

The fine adjustment knob is used to fine-tune the focus to get a more clear image.

「回回回 40x 100x

Using coarse adjustment knob at higher magnification may result in cracking of the slide or the lens or both. Because the gap between the objective lens and the slide is very little at higher magnifications (say 100X). The vertical path, moved by the lenses are significantly larger, in case of coarse focus than fine focus. Thus the chance of crashing the objective lenses is high, if we use the coarse focus with a 100X objective lens.