The rings are known as a zone plate.

这些环被称作波带片。

Using a zone plate instead of a mirror gets around this.

用波带片代替镜面在轨道运行。

Fresnel telescopes have not been developed in the past because the image formed by one that was large enough to rival a useful-sized reflecting telescope would be several kilometres from the zone plate.

过去，菲涅尔设计的望远镜还制造不出来，因为要想使衍射望远镜的大小和正常使用的反射望远镜大小相同，它所产生的图像就会距离波带片数千米远。

Using a zone plate instead of a mirror gets around this. Because the plate is flat, it can be made of plastic and folded up for launch. Size thus ceases to be an issue.

用波带片代替镜面在轨道运行。因为波带片表面是平的，他可以用塑料制作而成，然后折叠起来发射。而尺寸大小就不再是问题。

Extrapolating from these results, they think that an orbiting zone plate measuring somewhere between 15 metres and 40 metres across will be enough to distinguish the spectrum of an Earthlike planet at a distance of 30 light-years.

从这些结果推测，他们认为，一个直径在15到40米、并且在轨道上运行的波带片足够在30光年以外的距离分辨一个与地球相似的行星的光谱。