Objective Traditional optical systems typically employ multiple optical elements to correct aberrations, resulting in complex system architectures. Annular aperture optical systems achieve miniaturization and weight reduction by fabricating multiple concentric reflective zones on a single element to fold the optical path. However, the inherent central obstruction in such systems leads to reduced image contrast and edge blurring, thereby limiting imaging quality. To address the image degradation problem caused by central obstruction, this study proposes a method to suppress the impact of central obstruction on the imaging quality of annular aperture optical systems.

Methods To address the image degradation caused by central obstruction in annular aperture optical systems, this study analyzes the influence of the obstruction ratio on both the shape and energy distribution of the point spread function and on the modulation transfer function. An image degradation model based on central obstruction is constructed by incorporating the detector pixel integration effect. Building on this foundation, a regularization-based image restoration method utilizing gradient prior is proposed. Different regularization weights and prior parameters are selected, and the original image is iteratively solved using the Half-Quadratic Splitting method. Restoration quality is evaluated through subjective assessment and objective metrics, namely the Tenengrad function and average gradient values. The restoration effectiveness of the proposed method under various obstruction ratios is analyzed.

Results and Discussions Based on the analysis of image restoration effectiveness under various obstruction ratios presented in this study, an annular aperture optical system was designed with a focal length of 57 mm, an obstruction ratio of 0.71, an equivalent F-number of 1.25, and a semi-field of view of 4.95°. The proposed method was applied for image restoration, and the restoration results were quantitatively evaluated. The Tenengrad function value of the restored image increased by 1.319E–01, representing an improvement of 132.57% compared to the degraded image. Similarly, the average gradient value increased by 5.110E–02, corresponding to an improvement of 32.54%. These results validate the effectiveness of the proposed method.

Conclusions To address the image degradation issues of reduced contrast and edge blurring introduced by central obstruction in annular aperture optical systems, this paper establishes an image degradation model and designs an annular aperture optical system with approximately spatially invariant point spread function (PSF) characteristics. By integrating the proposed deconvolution regularization algorithm, the image degradation caused by central obstruction in annular aperture systems is effectively restored. In simulation, the Tenengrad and average gradient (AG) values of the restored scene image increase from 5.486E–02 and 1.228E–01 to 1.636E–01 and 1.684E–01, respectively. In physical experiments, the Tenengrad and AG values of the captured and restored scene image increase from 1.010E–01 and 1.570E–01 to 2.349E–01 and 2.081E–01, respectively. Compared to the simulation results, the percentage improvements in Tenengrad and AG values decrease from 189.83% and 38.39% to 132.57% and 32.54% in the physical experiment, yet a significant restoration effect is still achieved. The experimental results demonstrate that the proposed method can effectively mitigate the image degradation caused by obstruction in annular aperture optical systems, providing a new approach for suppressing the imaging impact of central obstruction in such systems.