Design of rigid endoscope objective lens system with adjustable viewing direction and depth of field

Endoscopic technology constitutes one of the cornerstones in the field of minimally invasive surgery. Nevertheless, conventional rigid endoscopes are subject to the limitations of a fixed viewing angle per device and a narrow depth of field range. To address these drawbacks, the design of a chromatic aberration-corrected endoscopic system with adjustable viewing direction and depth of field, as well as a corresponding image restoration algorithm was proposed, which was tailored for the abdominal surgical environment. The hardware architecture was composed of a miniaturized liquid prism, a solid objective lens group, and an electrowetting liquid lens. This objective lens achieved a minimum object-side resolution distance of 0.055 mm and an object-side angular resolution of 6.34 cycles per degree. The optical model of the proposed system was established. Simulation results indicate that on the basis of a 70° field of view (FOV), the system can realize dynamic viewing angle deflection of ±7.2° along both the x and y axes. Moreover, it is capable of clear focused imaging within a working distance range of 10 mm to 25 mm, while maintaining a modulation transfer function (MTF) value greater than 0.2 at 150 lp/mm. Compared with the original depth of field of the system, the observable depth was increased by approximately 68%. To rectify the additional chromatic aberration induced by viewing angle variations, an improved total variation-constrained image fusion technique was proposed, increasing the peak signal-to-noise ratio of the image by approximately 20% compared to traditional algorithms. The proposed system provides a novel approach to solving the problem that the viewing angle of traditional medical endoscopes cannot be flexibly adjusted.