In the context of microscopes, what does it mean for the objectives to be parfocal?

• A. The objectives can be used to adjust the intensity of light passing through the specimen.
• B. Each objective lens has a different focal length and requires complete refocusing when changed.
• C. Parfocal objectives are designed to increase the magnification beyond the maximum of the microscope.
• D. Once the specimen is focused with one objective, it remains nearly in focus when switching to another objective.

Answer: (D)

Verified step by step guidance

1. Understand the term 'parfocal' in microscopy: it refers to the design feature of objective lenses that allows the specimen to remain nearly in focus when switching between different objective lenses.
2. Recognize that microscopes typically have multiple objective lenses with varying magnifications and focal lengths.
3. Note that without parfocal objectives, changing from one objective to another would require significant refocusing to see the specimen clearly.
4. With parfocal objectives, minimal or no refocusing is needed after switching objectives, which saves time and maintains the clarity of the image.
5. Therefore, parfocality enhances the efficiency of microscopic examination by allowing smooth transitions between different magnifications while keeping the specimen in focus.