A very small lens aperture is employed to correct spherical aberration , but this severely limits the final resolution.
可以用一个非常小的透镜孔阑来校正球差，但这会严重地影响最终鉴别率。
2
It is hard to design for beam expander with high power and wide aperture required, because it is shorten length, larger aperture, as well as on axis and off axis aberration must be corrected properly.
The optical aberration difference between the biconvex Fresenl lens and the plane-convex Fresenl lens was investigated by designing a large aperture Fresenl lens.