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This case study presents an in-depth analysis of the optimization process for optical system design, specifically focusing on fixed-focus lenses. The study highlights the improvements made in lens design and material selection to enhance performance and manufacturability.
The double Gaussian structure is a popular design for fixed-focus lenses, characterized by its simplicity and high technical precision. Typically composed of six elements with meniscus lenses at the front and back, this nearly symmetrical structure effectively corrects aberrations such as coma, distortion, magnification, and chromatic difference of magnification. Despite its age, this design remains relevant due to its reliability and efficiency.
In the provided double Gaussian variant design, the first and fifth lenses are positive lenses with thin edges, which are prone to breakage during processing. The first lens has a diameter of 78mm and requires an edge thickness greater than 2.5mm, while the fifth lens, with a diameter of 48mm, needs an edge thickness over 2.2mm. The current design’s edge thicknesses fall short of these values, posing production risks. Expanding the outer diameters of these lenses is necessary to mitigate these risks and facilitate processing.
The original design employs conventional glass materials, including H-FK61 for the last lens. H-FK61, known for its high Abbe number and chromatic aberration correction capabilities, is soft and challenging to process, resulting in a low pass rate. Additionally, this glass, even with an AR film layer, is susceptible to scratches when exposed to the environment. Therefore, replacing H-FK61 with H-QK3L, which offers a similar refractive index, is recommended. This substitution, coupled with controlled minimum side thickness, results in a more robust and manufacturable lens design.
A well-designed optical system should minimize the impact of tolerances on performance. This case study examines a20X long working distance micro objective lens with ten elements, designed to approach the diffraction limit. However, the initial design’s aberration distribution is uneven, making certain lenses sensitive to tolerances. Tolerance analysis at MTF@200lp/mm reveals significant performance degradation in assembled products.
To address these issues, an additional lens was incorporated into the system, creating an eleven-element structure. This adjustment results in gentler light deflection and performance that meets the diffraction limit. The new design significantly reduces tolerance sensitivity and performance attenuation, with simulation results indicating that fine-tuning can yield high-performance lenses.
This case study underscores the importance of meticulous design and material selection in optimizing optical systems. By addressing issues such as edge thickness and material suitability, Shanghai Optics has enhanced the robustness and manufacturability of fixed-focus lenses. Furthermore, refining microscopic objective designs through structural adjustments has resulted in stable, high-performance lenses. These improvements not only mitigate production risks but also ensure consistent quality in final optical products.
Contact Shanghai Optics today! We’d be more than happy to discuss your projects and how to best bring them to fruition.