Focus on an area of sky where the fireworks will be, or on an object the same distance away.
可以对焰火即将绽放的那片天空对焦，或者找个与烟花相同距离的物体进行对焦。
You need to set your focus to infinity. Try focusing on a stable object in the distance.
你要把焦点设为无穷远，对准远处一处固定物对焦。
Once you choose a lens whose focal length is closest to the focal length required by your imaging system, you need to adjust the working distance to get object under inspection in focus.
一旦你选择一个镜头其焦距是最接近于你成像系统所需之焦距，你需要调较工作距离去获取观察目标物的焦点。
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