Endoscope Objective Optical System with Flat First Lens

The objective optical system is divided into multiple lens groups with different refractive powers (first lens group with negative refractive power, second lens group with positive refractive power, third lens group with negative refractive power). This segmentation allows each group to contribute differently to aberration correction, enabling compact design while maintaining high optical performance through coordinated action of discrete optical elements.

The patent employs cemented lens structures where lenses with different refractive indices and dispersion characteristics are bonded together (e.g., fourth lens with positive refractive power and fifth lens with negative refractive power forming a cemented lens). This composite approach corrects chromatic and spherical aberrations within compact dimensions by combining materials with complementary optical properties.

Different lens groups are assigned specific functions to correct different types of aberrations in different regions of the optical system. The first lens group with negative refractive power primarily corrects spherical aberration and controls the angle of view, while the second lens group with positive refractive power addresses coma and astigmatism. This localized correction strategy enables wide-angle imaging while maintaining high image quality across the entire field.

The patent employs an aperture stop positioned between lens groups to dynamically control the cone angle of incident light. By adjusting the aperture stop, the system can optimize the balance between wide angle of view and aberration correction, allowing flexible adaptation to different imaging requirements while maintaining optical performance.