## 1 Introduction
(**a**) Nonproliferative diabetic retinopathy (NPDR) with scattered hard exudates and small hemorrhagic spots around the macula. (**b**) Proliferative diabetic retinopathy with significant early vitreous hemorrhage. (**c**) Acute leukemia with a combination of flame hemorrhage, lint spots, and Roth spots. (**d**) Chronic leukemia with leopard-like changes due to choroidal infiltrate. (**e**) Stage III hypertensive retinopathy with arteriosclerotic changes, generalized coarctation, copper wires, scattered lint spots, and flame hemorrhages in the retinal arteries. (**f**) Infective endocarditis with central white hemorrhage in the fundus, known as Roth spots. properties of the human eye, it is also necessary to ensure that the optical system is safe for the human eye. (2) Image processing: The processing of fundus images is another important challenge in fundus camera design. Fundus images are often affected by various factors, so advanced image processing technology is required to improve image quality and the visibility and identification accuracy of lesion areas. (3) System integration and miniaturization: With the development of technology, people have put forward higher requirements for the portability and ease of use of fundus cameras. Integrating high-precision optics, image acquisition and processing systems, light source systems, and other auxiliary functions into a small, lightweight device is a challenging task. (4) Cost control: Cost control also needs to be considered while ensuring the performance of the equipment. Core components such as high-precision optical components and image processing chips are often costly, and how to reduce costs while ensuring performance is a practical challenge in fundus camera design. [PERSON] et al. designed a 39\({}^{\circ}\) field of view of visible light non-mydriasis fundus camera optical system, which resolved the 10 um structure of the fundus [7] and eliminated the stray light caused by the surface reflection of the omental objective lens group by polarization. The fundus retina illumination was uniform [7] but the imaging system was too long, reaching 265 mm. [PERSON] et al. designed a 40\({}^{\circ}\) field of view dual-light source fundus camera optical system [9], where visible light was used to shoot retinal images, near-infrared light was used for observation, the beamsplitter of visible light transmission and infrared light reflection were used to realize the dual-light source common beam path design, and corneal stray light was suppressed through the ring light source. The imaging system was 228 mm, so the length was still long, and the final design result was still relatively complex. In 2019, [PERSON] et al. from the University of Miami in the United States [9] developed a handheld fundus camera based on Shumei Pai and implanted the Linux operating system and OpenCV library into the system. Four fundus images with a field of view angle of 10\({}^{\circ}\) were stitched together to obtain images with a field of view of 16\({}^{\circ}\)[10]. However, it was easy to lose the details of the fundus in the stitching of the image, the composite image could be distorted, and the proportion of each tissue could not be truly reflected. In this context, our research presents a non-coaxial annular array illumination structure using aspherical lenses to reduce the total length of the system. This pioneering approach was designed to make the optical system compact. Our study was dedicated to facilitating the miniaturization of fundus cameras to match with components with different functions to realize the integration of functions and solve the problem of difficult and large volumes of stray light suppression in the traditional fundus optical system. We firmly anticipate that our contributions will propel advancements in the field, providing more detailed and accurate images tailored to practical applications.