The fundus camera used in imaging retina includes two parts:fundus imaging path with a positive focusing lens and annular Kohler illuminating path.We present a pupil joint equation and a focus equation based on the internal focusing manner to analyze its configuration.Using these equations,the configuration of the camera is given in detail.The design result of the fundus imaging path shows compact initial configuration at a total length of about 123 mm.The focusing range is-10-10 diopter,and the movement of the focusing lens is nearly linear at displacement of more than a sub-millimeter per diopter.
This letter shows that the human eye fundus tissue has higher reflectivity at the near-infrared (NIR) wavelength, and that some aberrations exist at the pre-optical system from cornea to vitreous. We design a NIR fundus camera with inner focusing, which can be applied to the -10D to 10D range of vision and has the advantage of ensuring the stability of image when is focused. Considered as Liou's eye aberration model, we correct the integrated aberration to ensure a 100lp/mm resolution when we complete the assembly and calibration of the fundus camera. Kohler illumination is also applied to obtain uniform fundus illumination. Moreover, we put forward a novel method for stray light elimination based on polarization switch, which inhibits ghost image formation near the focal plane when the illumination beam is reflected by the eyepiece surface. The result shows that this method is effective in ensuring an illumination uniformity of 80%, with the advantage of simple structure and easy assembly.
