折反式眼底相机光学系统设计

为控制传统眼底相机的杂光和鬼像,设计了一款40°视场、48mm工作距离的折反式眼底相机光学系统。设计了离轴反射式网膜物镜,引入了自由曲面以校正其离轴像差,成像物镜中采用两个自由曲面对网膜物镜的剩余像差进行校正。建立了一种离焦眼模型,用于优化成像光路,消除人眼像差对成像的影响,同时得到不同视度缺陷眼的成像光路。照明光路中使用3个相邻的环形光阑,减少了眼球光学系统反射的杂光。成像光学系统可在-10～+10m-1调焦,物方各视场分辨率为33lp/mm,系统畸变小于8.5%;照明光学系统在不产生鬼像的前提下,可均匀照明眼底,照度非均匀性在15%以内。实验表明,引入自由曲面的折反式眼底相机,有效地消除了杂光和鬼像,满足大视场和大工作距离的要求。

Design of optical system for catadioptric fundus camera

To eliminate the scatter light and central ghost in a classical fundus camera, the optical system of a catadioptric fundus camera with a field of view 40° and a working distance of 48 mm was designed. An off-axial reflecting ophthalmic lens with free form surfaces was designed to correct the off-axial aberrations. Two free-form-surfaces were introduced in the imaging objective system to correct the residual off-axial aberrations of the reflective ophthalmic lens. In the optimization of the imaging system, an eye model with varying defocuses was proposed to eliminate the negative effect of eye aberrations as well as to accommodate the eye with different refractive errors. Three adjacent illumination rings were introduced in the illumination part to avoid the undesirable light reflected by the eye optical system. Experiments show that the accommodation range of the system is between -10 m-1 and 10 m-1, the resolution at the object plane is 33 lp/mm across the entire field of view,and the maximum distortion is less than 8.5%.Furthermore, the illumination non-uniformity is less than 15% in the conditions without scatter light and central ghost. The designed catadioptric fundus camera with a free-form-surfaces show a satisfactory large field of view and a large working distance, and removes the undesirable scatter light and central ghost greatly.