焦距

Either of two fine mutually perpendicular lines that cross in the focus plane of an optical instrument and are use for sighting or calibration.

相交在一台光学仪器焦距平面的两条相互垂直的直线中的任何一条，用来瞄准或者校准。

An automatic focussing device that modifies the focal length of the lens systems in order to focus the same according to the distance from the telescopic spectacles to the object is allocated to the lens systems.

透镜系统配置有一个自动聚焦装置，它根据望远镜与对象的距离改变透镜系统的焦距使其聚焦。

The error analysis of stray light measuring instrument for optical system［J］.

长焦距光学系统杂光系数测量的新方法及其理论分析［J］。

B: I suppose it is out of focus.

我想是焦距的问题。

A: Perhaps it is out of focus too.

或许也是焦距的事。

I'm sure you got it out of focus

我肯定你没将它的焦距对准。

They begin by shaping the outer diameter of lens which takes only a few seconds.

这个叫前焦距计，用来测量镜片的光学精度的。

A new method of high aspect ratio and resolution zoneplate fabrication using both electron beam lithography and X ray lithography technology is described The zoneplate, composed of 10μm thick Au with 30 zones and outest zone width of 0 5μm, can be used as a focusing and chromatic dispersion device for 0 1～1nm harder X rays Results show that the zoneplate has contrast of 10 and above, resolution of 0 55μm, and focus length of 21 3cm for 8keV X ray

介绍了利用电子束和 X射线束双曝光技术制作大高宽比高分辨率的 X射线聚焦或色散元件的新方法(波长范围为 1～ 5 nm )。所制做的厚度为 10μm的 Au波带片具有 30个波带，最外环的宽度为 0 。5μm。实验表明：对 8ke V的 X射线来说，波带片的衬度大于 10 ，分辨率为 0 。5 5μm，焦距为 2 1.3cm。

Two convex lenses of equal diameter with a focal length of 3cm and 5 cm respectively have parallel light Rays passing through them.

想象假如没有透镜我们的生活会有什么不同？如下图所示： A 、 B 是两个口径相同的凸透镜，它们的焦距分别是3cm 和5cm。。

Close-up performance of the Summicron-M is on the same level as the performance at infinity setting actually infinity is that distance where the incoming light rays are parallel to the optical axis.

近摄表现与无穷远时相当(事实上，无穷远处的光线是平行光轴入射的。对多数镜头而言，大约100倍焦距的物距时，入射光满足这一条件)。

I didn't watch TV last night, because it .

昨晚我没有看电视，因为电视机坏了。

Since this year, in a lot of villages of Beijing, TV of elevator liquid crystal was removed.

今年以来，在北京的很多小区里，电梯液晶电视被撤了下来。