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Learn about Focusing the Microscope.
Focusing the Microscope
After seeing that an objective (low power) and an ocular are in place put a transparent or semi-transparent specimen on the stage, swing the mirror bar to the median line, take hold of the edge of the mirror and adjust it so as to illuminate the object as evenly as may be judged by looking directly at it. Focus the body tube down by means of the coarse adjustment until the objective nearly touches the cover glass, being careful not to touch it. Then with the eye at the eyepiece, focus up carefully with the coarse adjustment until the specimen comes plainly into view. Be careful not to pass by this focal point without noticing it. This is likely to occur if the light be too intense and the specimen thin and transparent. If the sliding tube coarse adjustment is used, focus carefully by giving the tube a spiral movement. When the object is brought fairly well into focus by means of the coarse adjustment use the fine adjustment to obtain the sharpest focus to bring out details. Do not expect too great a range in the fine adjustment. It is even more dangerous to focus down to any extent with the fine adjustment than with the coarse adjustment, because any impact of the front of the objective on the cover cannot be as easily felt. \Vhile moving the specimen about to observe different parts of it, it will be necessary to continually work the fine adjustment to keep the object in focus. It is always well to move the specimen when trying to get a focus, for without the movement one may be trying to focus upon a point where there is no object, and again, the moving object is more apt to be noticed as the lens comes into focus. It will be noticed during this movement that the microscope reverses the image, and that the specimen seems to move in the direction opposite to that in which it is moved. This, along with the fact that the microscope magnifies the movement as well as the specimen, is perplexing at first and makes it difficult to move the specimen just where it is wanted, and no farther. With practice comes the delicacy of movement which enables one to put the specimen just where he wants it. The beginner should always use the low power objectives and oculars first. The low power objectives have longer working distances and are not so apt to be injured. They always show a larger portion of the specimen and thus give one a better idea of the general contour. After obtaining this general idea the higher powers can be used to bring out greater detail in any particular part. If the objectives are par-focalized and centered on a nosepiece as described on page II, the change of objectives is made by simply turning one objective out of the optkal axis and the other into it without the necessity of re-focusing (except for a slight turn of the fine adjustment) and again hunting up the particular spot desired, for if this spot is in the center of the field of the low power it will be somewhere in the field of the higher power. It is too much to ask of the maker that the lenses be made absolutely parfocal and centered. The delicacy of the centering can be appreciated when the magnification and the extremely small portion examined is considered. When the objectives are not thus fitted to the nosepiece, re-focusing and again hunting up the object are necessary. In doing so we repeat the caution to always focus up before turning the nosepiece. When no revolving nosepiece is used the change of objectives .means the unscrewing of one and the screwing of the other into its place, and refocusing as before.
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Microscope Technique 
