The first part of the microscope that should first be used to adjust the focus when starting with the lowest power lens would be the coarse adjustment knob.
There are two knobs in a typical light microscope with which objects on slides can be brought into focus:
The 2 knobs are used to adjust the stage to either bring it up towards the objective lens or down away from them. The coarse adjustment knob, however, moves the stage a considerable distance with each turn. The fine adjustment knob, on the other hand, only moves the stage very little with each turn.
The lowest power lenses are often short. Hence, using the coarse adjustment knob is ideal in order to quickly bring objects on slides into focus.
The fine adjustment knob comes highly recommended at high objectives because high objectives lenses are usually long and using the coarse adjustment knob can lead to a breakage of the slide by the lens.
More on bringing objects into focus on a microscope can be found here: https://brainly.com/question/24319677
