Large-field telescopes play a significant role in cutting-edge astronomical research fields, such as time-domain astronomy and cosmology. For such telescopes, ensuring symmetrical and uniform imaging across the entire field-of-view (FoV) is pivotal, particularly for areas such as astronomical photometry and astrometry. However, conventional image quality evaluation methods for telescope optical systems have mainly focused on imaging spot size. Other alternative methods, such as ellipticity based methods, also face the challenges of high computational requirements and limited assessment parameters. In addition, establishing a coherent link between the telescope structure and research domains such as photometry has remained a challenge. In response to these challenges, we introduce an assessment approach termed the ray tracing, spot-vector index, and angle (RSVA) approach. This approach offers a fresh perspective on optical systems, prioritizing the depiction of imaging spot shapes. It acts as a valuable supplement to traditional methods and has been effectively employed to analyze four 1-m aperture telescopes with an f-ratio of 3 for a 3 deg FoV. Building on this foundation, the RSVA can be further expanded to explore other research avenues, including exploring the interplay between photometry and telescope systems and guiding large FoV optical design.