Final answer:
A focal-spot size of 0.3 mm or smaller is crucial for magnification radiography, as it allows for greater magnification. However, there is a trade-off between magnification and the chances of photodegrading the specimen.
Step-by-step explanation:
In radiography, a focal-spot size of 0.3 mm or smaller is essential for magnification. When using a lens with a smaller focal length, a greater magnification can be achieved. This is because the focal point spreads to become a focal spot with the size of the spot decreasing with increasing numerical aperture (NA). The intensity in the focal spot also increases with increasing NA, which can be beneficial for imaging, but there is a trade-off between magnification and the chances of photodegrading the specimen.