But focusing on close objects involves contraction of muscles controlling the shape of the eye's lens. And one possibility is that "this constant contraction may stretch the eyeball.
目前没有研究显示为什么大量阅读会导致这一结果，但是由于长时间聚焦近处的物体需要眼部肌肉持续收缩以保证视网膜保持需要的形状，因此这种眼肌的持续收缩状态可能会使眼球受到拉伸，长期如此，其原有形状可能会被永久地改变，从而导致近视产生。
While he could mount the lens, if it was not focused at it's closest regular focusing distance, the close up range was inoperative due to some sort of internal body restrictions.
他能装上镜头，如果不能在常规对焦区间的最近端对焦，那么近距对焦就不能工作，原因是机身内部的某种限制。
THEN pull the focusing barrel out slightly, and the lens barrel can be swung over farther to the left, to get into the close focusing range.
然后轻轻将镜头的调焦筒拉出，镜筒就可以继续向左转动以获得更近的对焦距离。
THEN pull the focusing barrel out slightly, and the lens barrel can be swung over farther to the left, to get into the close focusing range.
然后轻轻将镜头的调焦筒拉出，镜筒就可以继续向左转动以获得更近的对焦距离。
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