If the eyeball is too long, the eye's lens can't focus the light in the right part of the retina to process images clearly.
如果眼球太长，那么眼睛的晶状体就无法将光线聚集在视网膜的正确位置，人类也无法接收到清晰的图像。
这是个长焦距镜头。
In this experiment, we use two gratings with the same frequency to generate Moire fringes and use them to measure the long focus length of lens.
本实验是利用两块空间频率相同的黑白光栅产生的莫尔条纹来测量长焦距透镜的焦距。
焦距长底随透镜的厚度而变化。
Firstly, a telescope system is made up with a concave lens and a long-focus convex lens, by which the angle of the parallel beam from the collimator can be change.
该方法借助一个焦距较长的凸透镜与被测凹透镜组成无焦系统，可以使准直管出射光束的张角发生改变；
Firstly, a telescope system is made up with a concave lens and a long-focus convex lens, by which the angle of the parallel beam from the collimator can be change.
该方法借助一个焦距较长的凸透镜与被测凹透镜组成无焦系统，可以使准直管出射光束的张角发生改变；
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