Spherical aberration and coma are primarily dependent on which factor?

Spherical aberration and coma are optical phenomena that arise due to the geometry of lenses and how they focus light. The size of the pupil plays a significant role in these aberrations because it determines the amount of light that enters the optical system and how light rays are focused.

When the pupil is larger, it allows more peripheral rays of light to enter the system, which can lead to an increase in spherical aberration. This occurs because these rays, especially at the edges, do not converge at the same point as the rays that pass through the center of the lens. Similarly, coma can be exacerbated when the pupil is large since it highlights the variations in focus across the lens's aperture, causing images of points of light to appear elongated or distorted.

The other factors—lens shape, lens thickness, and angle of incidence—also contribute to optical performance but are not as directly related to the primary formation of spherical aberration and coma as pupil size. For example, while the shape of the lens can influence how light is refracted, it is the size of the pupil that determines how much light enters and how aberrations manifest in practical applications. Thus, controlling the pupil size is crucial in minimizing these aberrations in optical systems.