Four kinds of laser source are used to measure the diffractive efficiency of Fresnel lens.
使用四种不同光源，对菲涅耳透镜的衍射效率进行测试。
2
There are four kinds of lens shapes, which do you like best?
我们有四种镜片形状，您最喜欢哪种？
3
On account of four distortions such as signal lag, radial distortion, eccentric distortion and thin lens, etc. a precision distortion correction model is established.