Final answer:
When switching to magnification mode in fluoroscopy, an increase in exposure factors is necessary due to a shift in focal length, resulting in a smaller field size and the need for more radiation to ensure image quality.
Step-by-step explanation:
During fluoroscopy, when changing from normal to magnification mode, an increase in exposure factors is required because the focal length changes. Magnification mode accomplishes an increased image size by effectively zooming in on a smaller area of the patient's body, which results in a reduced field size on the image receptor. Since the same amount of X-ray photons are now concentrated on a smaller area, to maintain image quality and brightness, a higher dose is needed to compensate for the decreased field of illumination. This ensures the resulting image has sufficient brightness and contrast for diagnostic purposes.
To obtain greater angular magnification in magnification mode, it is often necessary to use a combination of a long focal length objective and a short focal length eyepiece. This is because the greater the angular magnification M, the larger an object will appear when viewed through a device like a telescope or a fluoroscope, allowing for more detail visibility. However, higher magnification often comes with the trade-off of requiring more radiation to maintain image clarity and brightness.