Focus controls

English

The focus controls on a good microscope are coaxial, so the fine focus and the coarse focus are easily controlled by one hand, and you don't have to move your eyes off the eyepieces to look for them. They will also be placed low, so you can rest your arms comfortably on the table while using them, to prevent fatigue during prolonged use.

Usually there will be identical controls on both sides of the microscope, making it convenient for left or right handed users, and allowing one hand to be on the focus controls while the other is on the stage controls, so the eyes never have to look up.

The focus controls will also generally have a slip clutch, so that they can't be forced too far in either direction. This protects the slides and the objectives from damage, as well as the rack and pinion of the focus controls. In addition to this protection, high power objectives often have spring loaded barrels, so that if they are brought down onto a thick subject by accident, they will retract. Don't rely on this, as they can only retract a small amount.

The focusing can move either the stage or the microscope tube. Generally, in modern professional microscopes, the stage moves up and down, and the tube is firmly anchored to a large heavy arm and base. This allows heavy cameras to be mounted on top of the tube.

The focus controls often have an adjusting ring that controls how difficult it is to move the focus. If you find that the focus shifts as you work, this control can be tightened to prevent unwanted or accidental focus adjustments.

The fine focus knob often has rulings on it. This makes it easier to create stacked images for greater depth of field, as you can move the focus in precise increments.