What is the definition of par focal in microscopy?

The term "parfocal" in microscopy refers specifically to the ability of a microscope to remain in focus when switching between different objective lenses. This means that once a specimen is initially brought into focus using one objective, changing to another objective lens will require only minor adjustments to the focus, rather than needing to refocus entirely. This feature is particularly beneficial in microscopy as it allows for smooth transitions between lenses of varying magnifications, helping to maintain the clarity and sharpness of the specimen being examined without significant interruption.

While other options discuss interesting features of microscopes, they do not accurately capture the essence of what parfocal means. For instance, increasing magnification without loss of detail pertains to the optical quality of the lenses but does not specifically address the focusing characteristic. Similarly, three-dimensional viewing and reducing time needed for focusing may refer to additional capabilities of certain microscopes but do not define the parfocal property. Hence, the correct definition emphasizes the practicality and usability of microscopes when examining specimens at different levels of magnification.