How does numerical aperture affect the resolution of a microscope objective?

The numerical aperture (N.A.) is a critical measure of a microscope objective's ability to gather diffracted light and resolve fine details in a specimen.12

How Numerical Aperture Affects Resolution

When light interacts with an object, it undergoes diffraction, with finer structural details causing light to diffract at wider angles. The resolution of a microscope is fundamentally limited by the objective's ability to collect these diffracted waves.12

• Light Collection: The N.A. represents the sine of half the angle of the cone of light accepted by the objective, multiplied by the refractive index of the medium between the specimen and the lens. A higher N.A. allows the objective to capture a greater number of diffracted waves.231
• Reconstruction: Because the ability to reconstruct an image depends on the amount of diffracted light captured, a higher N.A. directly enables the resolution of finer details.1
• Limitations: If an objective has an insufficient N.A., the finest details of the object will not be resolved, regardless of the magnification used; attempting to enlarge these details further results in empty magnification.1