焦距

Bring the subject into focus if you want to have a good picture.

要想拍出好的照片，必须给被摄物对好焦距。

Despite the fact that convergence, without exaggeration, goes by seven-mile steps and already appeared the first cell phones with the built-in 10 mega-pixel camera, the creation of the thin objectives, which possess at the same time high candlepower and capable of changing focal length, it remains one of the main problems.

尽管事实上收敛，毫不夸张地说，不用了7英里的步骤和已经出现的第一个手机内置10万像素的摄像头，建立了薄的目标，拥有在同一时间高烛光和能力改变焦距，但它仍然主要问题之一。

Image quality is OK in the center but a bit soft at the edges. This will be more obvious in the following comparisons with the 24-70/2.8L at 24mm, 35mm and 55mm.

中央的图像质量很好但是在边缘有些柔，当和24-70/2.8L在24mm， 35mm， 55mm焦距比较时更为明显。

Focal length is one of the most important optical characteristic parameter of optical lenses and optical instruments.

焦距是光学透镜和光学仪器的重要光学特性参数。

At last, guided by the theoretical calculation mentioned above, a series of experiments were carried out. The wavefront distortion of a plano concave lens was measured. The total error was less then 8%. This certified the measured results of the interferometer. The wavefront distortion of a one-side pumped zigzag slab gain medium in different pumping power was measured.

最后，在上述理论计算的指导下，进行了一系列波前检测实验：对一个焦距已知的平凹透镜所产生的波前畸变进行了检测，总的测量的误差小于8%，验证了系统测量结果的准确性；测量了一个单侧泵浦的之字形板条增益介质，在不同泵浦功率下的波前畸变情况。

As to the remaining parameters, two methods are developed: first, accepting that the projection function complies with a circular function within at least a part of a given field of view, constrained by the obtained object-to-image radial mapping and a constant focal length, the best-fitting point of the optical origin is tested along the optical axis; secondly, referring to the postulation of the exclusively bilateral mapping between an imaged point and its scenic sight ray, a measuring technique is developed to survey the world coordinates which will fabricate a projecting path to the imaged points located on the imageable region of the image plane in order to directly model the projection geometries involved.

而针对其余参数本文提出两种解题方法：其一是根据『在「部分视野角范围」内，鱼眼相机的投射模型符合一典型的「圆形函数」』以标靶实体与其影像尺寸为限制条件，测试光学轴上的最佳视觉参考点、鉴定最适当的投射模型、焦距、及有效的视野角度范围。其二是根据『一视野线排他性地与对应「呈影点」一一映射』参考一呈影点来搜寻空间中对应视野线的绝对座标后，据以演绎相机内部影像形成的模型。

The collimator neutron flux is drawn from the horizontal channel by the use of SPRR-300 as a neutron resource. The convector made of 6LiFZnS and the long focus professional twilight lens with the small field of view are used, and the digitalized CCD camera is developed by the use of scientific grade CCD chip, the double thermocouple refrigeration and 14bit A/D convector. The image grabbing, processing and analyzing software of double bytes has been developed by the use of Visual C++ and C++ Builder, and the facility of anti-radiation for CCD is set up.

采用6LiFZnS材料中子转换屏、长焦距、小视场专用微光镜头等光学组件，利用科学级CCD芯片、两级热电偶制冷技术、14bit模数转换技术研制了数字CCD摄像机，采用Visula C++和C++ Builder为工具，开发了双字节图像采集处理分析软件包，并设计了成像系统辐射防护装置，构成了热中子数字成像系统。

As shown, a thin convex lens with focus length 10 cm and a concave

如上图所示，一焦距为10 cm的薄凸透镜和一半径为20 cm的凹球面反射镜共轴。P点球心

In contrast to the experimental report by Cao and Evans, we found that the crack would extend under a cyclic electric field below the coercive field by the in-situ observation through a long focal length optical microscope.

不同于Cao和Evans的实验报道(矫顽电场以下，裂纹不发生扩展)，我们在通过长焦距显微镜实时观测了循环电场的幅值低于矫顽电场时，铁电陶瓷中疲劳裂纹扩展的规律。

Referring to the function of cylindrical lens and the principles of holographic optical elements, we make this holographic element, which can achieve the optical function of cylindrical lens, and have the advantage of large-scale, short focal length and well-distributed light energy, in order to meet the requirements of laser direct writing synthetic holograms.

实验结合激光直写合成全息拍摄时所需柱面透镜的功能，参考全息光学元件的制作原理来制作图像柱面压缩全息光学元件，实现柱面透镜的光学功能，并使元件具有大面积、短焦距、会聚光均匀分布的特点，满足激光直写合成全息拍摄对图像的需求。

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。