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5.2 (Pre-) Focusing
In order for an object to be observed, it must be at the correct distance from the lens
so that a sharp image can be obtained.
To find this distance initially (without any other presettings of the microscope), bring
the objective with the lowest magnification into the beam path, look with the right eye
through the right eyepiece and turn the coarse adjustment knob slowly at first (
see
illustration
).
The simplest method for this would be to bring the stage (also using the coarse drive)
to just below the lens beforehand and then slowly lower it. As soon as an image (no
matter how sharp) can then be seen, the correct sharpness should only be set with the
fine drive.
Torque adjustment of coarse and fine drive
Next to the left adjusting wheels of the coarse and fine drive is a ring which can be
used to change the torque of these wheels. Turning clockwise decreases the torque
and turning counterclockwise increases the torque.
This function can be used to facilitate the focus adjustment on the one hand and to
prevent the object stage from sliding down unintentionally on the other hand.
Important
To avoid damage to the focusing system, never turn the left and right dials of the coarse
and fine focus knobs in opposite directions at the same time.
