Objective Confocal laser scanning microscopy (CLSM) is a powerful tool in advanced biomedical imaging, as it reject out-of-focus light and reconstruct high-contrast images with sub-cellular resolution. However, conventional microscope objectives often face trade-offs among numerical aperture (NA), field of view (FOV), and working distance (WD), making them less suitable for high-etendue biological imaging that demands both resolution and coverage. In addition, large-FOV objectives are typically prone to aberrations that degrade image fidelity. To overcome these challenges, we report the design of a high-performance microscope objective optimized for large-FOV, high-NA, and long-WD confocal imaging. Based on a modular, systematic design methodology, the objective achieves a 12 mm FOV, 0.5 NA, and 12 mm WD while maintaining diffraction-limited performance across the visible spectrum. The adoption of a retrofocus architecture combined with distortion correction further ensures stable imaging quality across the full field. This work provides an effective design route for high-efficiency, high-resolution imaging under demanding optical constraints, and provides a reference for future developments in complex objective lens systems.

Methods We introduce a design methodology that integrates modular systematic design with targeted distortion correction for large-FOV, high-NA microscopy. The design process begins with the selection of an initial structure incorporating key modules, in line with modular design principles. These modules are then strategically combined and optimized in ZEMAX to obtain an intermediate configuration that closely approaches the target specifications. This intermediate solution serves as the basis for subsequent global and local optimization. Compared with conventional design approaches, the proposed strategy not only guarantees optical performance but also significantly improves design efficiency and reduces reliance on designer experience.

Results and Discussions The optimized microscope objective comprises 17 lens elements arranged in three groups (Fig.10). Through systematic modular design and iterative optimization in ZEMAX, the final optical configuration achieves diffraction-limited imaging performance across the entire visible spectrum and the full 12 mm FOV. Chromatic performance is well controlled: The maximum axial chromatic aberration (ACA) is less than 4 µm, and axial color curves for different wavelengths are tightly clustered, confirming effective chromatic correction. Distortion is effectively suppressed, remaining below 1% across the field. As illustrated in the grid distortion diagram (Fig.12), deviations between ideal and actual image points are minimal, indicating negligible impact on image fidelity. Furthermore, the modulation transfer function (MTF) results validate the high-resolution imaging capability of the objective. The full-field MTF curve approaches the diffraction limit across all field positions (Fig.13), demonstrating that the system achieves excellent imaging quality throughout the entire field of view. These results confirm that the design meets the stringent requirements of high-etendue, high-resolution confocal imaging.

Conclusions This paper presents the design and realization of a high-etendue confocal microscope objective featuring a 12 mm field of view and a numerical aperture of 0.5, specifically tailored to meet the requirements of high-resolution, large-FOV confocal imaging systems. Such imaging systems are increasingly critical in fields like biological research, where both imaging speed and resolution are critical for capturing dynamic processes and fine structural details. To achieve these demanding specifications, the design employs a systematic strategy that integrates modular optical design principles with a retrofocus configuration. This configuration facilitates an extended working distance and favorable optical power distribution, balancing aberration control with system requirements. In addition, a dedicated distortion-correction scheme further ensures accurate image reproduction across the field. Starting from a carefully chosen initial structure composed of key modules, the design progresses through multiple stages of global and local optimization in ZEMAX, yielding a reproducible framework for complex optical system development. The finalized objective lens demonstrates outstanding optical performance, achieving diffraction-limited imaging quality throughout the entire visible spectrum and across all field positions within the 12 mm FOV. These results confirm the system's ability to maintain high contrast, low aberration, and excellent resolution across a large field of view.