The IOR is razor sharp within 60% of the field, then, toward the edge, degradeing, first slowly and then, close to the edge, more rapidly, were the image quality becomes poor.

• IOR在60%25内是如剃刀削般轮廓分明，再移向边缘就降低等级了，开始是慢慢的，靠近边缘时急剧下降，图像质量变很差。