what does the coarse adjustment knob do on a microscope

The coarse adjustment knob on a microscope is responsible for rapidly adjusting the focus of the microscopes objective lens to bring the specimen into focus. It is used for initial focusing and moves the stage up and down noticeably, changing the level by centimeters. The coarse adjustment knob is usually located along the lower middle part of the arm of the microscope and is the bigger of the two knobs, located closest to the arm of the microscope. It is generally used when viewing specimens with a scanner objective (4X) .