Camera lenses have two general attributes: f-stop and focal length.
照相机镜头有两项一般属性：f制光圈和焦距。
This is the ratio of the focal length of the telescope to its aperture.
这是指望远镜的焦距与其孔径的比值。
Keep in mind that changing focal length will require refocusing in most zoom lenses.
要注意的是，对于大多数变焦镜头来说，焦距改变了，就得重新对焦。
Smaller sensors 'crop' the scene and make a lens appear to have a longer focal length.
更小感光元件会使得镜头产生更长焦距的效果。
Two lenses of focal length 10 cm have a combined focal length of 5 cm.
两个焦距都是10厘米的透镜形成的组合透镜焦距为5厘米。
The focal length of the camera lens plays an important role in photo criteria.
摄影机镜头的焦距在摄影规范中起着重要的作用。
The focal length of the camera lens plays an important role in photo criteria .
摄影机镜头的焦距在摄影规范中起着重要的作用。
The diameter of a sphere is four times the focal length of a concave mirror cut from it.
凹面镜如果是从圆球上切下来的，圆球的直径会是凹面镜焦距的四倍。
At present, some difficulties are encountered in measurement of long focal length of lens.
目前，透镜长焦距的有效测量还存在一些难题。
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。
After analyzing why the focal length changes, I give an automatic focus algorithm controlled by computer.
对自动聚焦问题，分析了焦距变化的原因，给出了计算机控制的自动聚焦算法。
We can therefore solve the problem by using different focal length in the process of tracking measurement.
如果能在跟踪测量过程中改用不同的焦距就能解决此问题。
For example, the focal length of an 8" (203.2mm) aperture with a focal ratio of f/10 would be 203.2 x 10 = 2032mm.
比如，孔径为8英寸(203.2mm)，焦比为f/10的透镜，其焦距为203.2x 10 = 2032mm。
A new method of microlens focal length measurement by rotation method based on grating diffraction is introduced.
介绍了一种利用光栅的多缝衍射分光代替传统转角法的角度测量的微透镜焦距测量方法。
A new method of measuring the monochrome focal length of lens is given from the single slit diffraction principle.
根据单狭缝衍射原理，提出了一种测量透镜单色焦距的新方法。
FLIR – The large aperture enables a longer focal length, which provides higher resolution without losing sensitivity.
大孔径允许更长的焦距，从而在不损失灵敏度的情况下，提供更高的分辨率。
It can be used to really evaluate the optical performance and imaging characters at any focal length of a zoom system.
可借助该程序对变焦系统任意焦距位置的光学性能和像差特性进行实时评估。
Or, you can calculate the exit pupil by dividing the focal length of the eyepiece (in mm) by the focal ratio of the telescope.
或者，你还可以将目镜的焦距除以望远镜的焦比来得到出瞳尺寸。
For example, a telescope with a focal length of 2000mm has twice the power and half the field of view of a 1000mm telescope.
比如，与焦距为1000mm的望远镜相比，2000mm焦距望远镜的放大率和视场范围分别是前者的2倍和1/2。
The reason for this is that as we know, longer focal length lenses magnify the image, but they also magnify the camera shake.
正如我们前面所学，更长的镜头焦距虽然放大了图像，但同样增加了镜头抖动。
This paper puts forward a dynamic calibration method for the focal length of the spacecraft's relative state measure system.
提出了一种航天器间相对状态光学测量系统焦距的动态校准方法。
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。
Digital SLRs with a lens focal length of 300 to 400mm are recommended, but you can get away with a decent compact with a 10x zoom.
推荐使用带有300 - 400毫米镜头的数码单反相机，但如果有一架有10倍变焦镜头，性能良好的小型相机也可以。
On the basis of thin-lens focal length measurement experiment, the imaging law of refraction-reflection system was further studied.
在薄透镜焦距测定实验的基础上，进一步讨论了折射反射系统成像的规律。
If you know the focal ratio but not the focal length, you can calculate it: focal length is the aperture (in mm) times the focal ratio.
如果你不知道焦距，只知道焦比(focalratio)，你可以通过这样计算的得到焦距：孔径(单位是mm)乘以焦比就是焦距。
Camera shake rule: The slowest shutter speed at which you can safely handhold a camera is one over the focal length of the lens in use.
手持拍摄时，最低安全快门速度为所用镜头焦距的倒数，低于这一速度，相机震动可能导致照片的锐度下降。
Camera shake rule: The slowest shutter speed at which you can safely handhold a camera is one over the focal length of the lens in use.
手持拍摄时，最低安全快门速度为所用镜头焦距的倒数，低于这一速度，相机震动可能导致照片的锐度下降。
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