In: Anatomy and Physiology
If after focusing low power, you need to use the fine adjustment to focus the specimen at the higher powers, the microscope is said to be _
In the low power, there is a wide field of view. This view narrows when the high power is used after low power. The magnification of the specimen also increases. Hence, the view becomes out of focus. In order to bring this view, in focus, the object has to be brought in the center. The fine adjustment is moved slowly till the view becomes focused. The sharpness of the specimen is focused. However, Parfocal microscopes remain in focus even when the objectives are changed by user. Only small adjustments are required to bring sharpness to the image.
When the low power is replaced by the high power objective, the microscope is said to be parfocal when there is no or minimal adjustment is done to bring the specimen in focus. Thus, in objectives can be interchanged, without changing the focus much. The fine adjustment can do fine focusing changes when the objective is changed to high power.
Right choice: parfocal.