Which statement best describes a fixed focusing system's adjustability during imaging?

• A. Focal depth is adjustable
• B. Extent of focusing is adjustable
• C. Neither is adjustable
• D. Both are adjustable

Answer: (C)

Fixed focusing systems are designed to produce a sharp image at one predefined distance without any user changes. That means the focal depth—the distance at which the image is most sharply focused—cannot be altered. It also means the extent of focusing, or the range over which objects stay acceptably sharp (the depth of field), is determined by the fixed optical design and isn’t adjustable during imaging. So, neither the focal depth nor the focusing range can be changed on such a system. If you need to image subjects at different distances, you’d switch to an adjustable focusing setup or adjust the setup itself rather than expect the fixed system to adapt.