G5系列提供额外的Z轴的焦点透镜元件的调整，以补偿不同高压光学厚度。
The G5 Series provides additional Z-Axis adjustment of the focus lens cell to compensate for varying High-Pressure Optic Thickness.
就是从透镜(或者主反射镜)到焦点的距离，通常单位是毫米(mm)。
This is the distance (usually in mm.) from the lens (or primary mirror) to the point where the telescope is in focus (focal point).
我在故事中谈到开普勒，不是因为他解释了星球运行规律，而是因为他解释了光如何在透镜中发生折射。正是他首创了focus(焦点)这个词。
He comes into my little story here because it was he, in explaining not how planetary motion worked but how light bent through lenses, it was Kepler who coined the term focus.
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