Final answer:
The numerical aperture (NA) of a lens is a measure of its ability to resolve fine detail. It is calculated using the aperture angle, which is defined as the half of the acceptance angle. A higher numerical aperture indicates a lens with better resolution.
Step-by-step explanation:
The numerical aperture (NA) of a lens is a measure of its ability to resolve fine detail in an object being observed. It is calculated using the aperture angle defined as the half of the acceptance angle. The acceptance angle refers to the maximum angle at which the lens can gather light and still contain it within the lens.
The NA is derived by mathematical formula and is commonly used in microscopy to quantify the resolving power of a lens. A higher numerical aperture indicates a lens with better resolution, as it can capture more light and resolve finer details.