The first shot was taken with a short focal length (around 70mm) and from a relatively close distance and the background looked quite far away and small.
第一张焦距约70 mm，在相对近的距离拍摄，背景看起来很远而且很小。
The focal length you need depends on your distance from the burst and what you're trying to capture.
你所需要的焦距取决于你和被拍摄焰火间的距离，以及你想捕捉到怎样的画面。
Using a longer focal length and photographing stars far from the north star increase the distance stars will move across the image.
使用长焦镜头拍摄远离北极星的星星，会增加星星在相片上移动轨迹。
If you know the FOV, sensor size, and working distance, you can compute the focal length of the lens you need using the following formula.
如果你知道视野FOV，感应器大小，和工作距离，你能用以下之方程序去计算你所需之镜头的焦距。
A lens is primarily defined by its focal length. Figure 4 illustrates the relationship between the focal length of the lens, field of view, sensor size, and working distance.
一个镜头的基础定义是其焦距，图4图示出镜头焦距，视野，感应器大小，和工作距离间之关系。
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。
It is shown that by changing the focal length of focal lens and the distance between the axicon and the lens, the center of dark of the bottle beams can be altered effectively.
这些结果表明，改变聚焦透镜的焦距和聚焦透镜到轴棱锥间的距离以及光阑半径，可有效地改变局域空心光束的暗中空区域。
The influences of pump energy, focal length and distance between fiber and lens on SBS reflectivity and waveform in multimode fiber are investigated theoretically and experimentally.
从理论和实验上研究了不同焦距下泵浦能量以及透镜与光纤间距对多模光纤中的SBS能量反射率和脉冲波形的影响。
Used to observe the details of a simple visual objects, optical devices, is the focal length than the distance between eyes, as much out of the convergence lens.
用来观察物体细节的简单目视光学器件，是焦距比眼的明视距离小得多的会聚透镜。
Notice the difference in the apparent distance of objects that each focal length produces.
注意每种焦距所产生的物体视距的差异。
This works for all apertures and focal lengths, but the smaller the aperture and the shorter the focal length, and the greater the distance you shoot at, the greater the depth of field.
这在任何光圈和焦距上都适用，只不过光圈越小、焦距越短，景深越大，你能够拍摄的清晰长度就越大。
This works for all apertures and focal lengths, but the smaller the aperture and the shorter the focal length, and the greater the distance you shoot at, the greater the depth of field.
这在任何光圈和焦距上都适用，只不过光圈越小、焦距越短，景深越大，你能够拍摄的清晰长度就越大。
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