An optical imaging system's resolving power is primarily constrained by diffraction, which is further impacted by optical aberrations. The impact of primary spherical aberration on the resolution of two closely spaced lines when the system's aperture size is decreased is the main topic of this study. The wavelength of light and the aperture diameter determine the minimum resolvable distance between two objects, according to the classical criterion put forth by Lord Rayleigh. Diffraction effects become more pronounced as the aperture decreases, resulting in a wider intensity distribution in the image plane and worse resolution.

Aberrations cannot be disregarded in real-world optical systems. Among these, fundamental spherical aberration—which is explained in Ludwig Seidel's classical aberration theory—contributes significantly to the deterioration of image quality. Because of this distortion, rays traveling through various aperture zones focus at various axial points, producing a blurry image with less contrast. In this paper, intensity distribution principles are used to investigate the combined effects of spherical aberration and aperture reduction on two-line resolution. The findings demonstrate that spherical aberration

greatly increases the diffraction-induced light spreading, increasing the overlap between two lines' pictures. As a result, when the aperture size lowers, the system's resolving power rapidly declin.The study emphasizes how crucial it is to reduce spherical aberration and maximize aperture design in order to improve resolution in contemporary optical imaging systems.

Keywords

Two-line resolution, Shrink aperture, primary spherical aberration, Point spread function, Apodisation, Optical, imaging systems