论广告摄像中的视像控制(下)

⒊视场角控制所谓视场角,就是镜头视角,它指摄像机摄像管画面对角线两端与镜头构成的角度,或者指景物画面对角线两端与镜头构成的角度。镜头的视场角越大,在同等距离拍摄的景物范围也就越大。从镜头视场角定义知道,镜头视场角的大小与摄像管的画面大小和镜头的焦距长短有关,由于摄像机内的摄像管画面大小一般固定不变,因此拍摄时视场角的大小实际上由镜头焦距的长短所决定,焦距越长,其视场角越小;焦距越短,其视场角反而越大。     

完全解析视场角度

正当你进行取景的时候,焦距并不是唯一的决定因素。Marcus Hawkins将为你进行详细的解释……本月你将学到镜头和感光元件尺寸是如何影响视场角范围的如何快速计算出35mm等效焦距为什么取景框里显示的不是完整的画面什么是视场角?视场角是衡量一支相机镜头能够"看到"的最大视野范围的标度,通常以角度作为单位。很明显,决定视场角的关键在于镜头焦距,焦距越长的镜头视场角越小。举例来说,一支200mm的镜头的视场角大约为12度,而一支20mm的镜头的视场角则要宽广的多,在全画幅相机上大约为94度。如果是变焦镜头的话,视场角则是随着焦距变化而变化     

基于衍射面的双目投影头盔光学系统设计

为满足双目头盔显示器对大视场的要求,对它进行了改进.设计了以微液晶显示器为图像源,有效焦距为35mm,出瞳距离为23mm,出瞳直径为12mm,视场角为40°的头盔投影显示器.该系统由一组双高斯透镜,一个半透半反镜和一个回射屏组成.回射屏的使用使双目设计的视场有效提高,畸变明显降低;衍射面的引入,使系统在尺寸和重量上有明显的减少,像质进一步提高.该系统投影镜头部分重量仅为6.8g,最大镜头直径为16.8mm,完全满足双目设计的要求.目视系统中需重点校正的像散和垂轴色差的最大值分别为0.32mm和13.1μm,最大畸变不足0.1%.选用分辨率为1024×768、像素尺寸为25μm的图像源,系统分辨率满足图像源的要求.     

用于大截面传像光纤束的折衍混合光学系统设计

在大截面传像束前置光学物镜设计中,采用“负-正”型式的像方远心光路结构,很好地解决了镜头轴外像差校正和像面照度均匀性问题,同时使镜头结构紧凑、小型化。给出了前置物镜设计实例:工作波长0.8~1.1μm,焦距5mm,相对孔径为1:3.84,光学长度为47mm,视场角为60°。在光学耦接镜设计中采用物方远心光路结构,引入二元光学透镜,通过理论计算和ZEMAX光学软件优化,给出工作波长0.8~1.1μm,焦距33.6mm,光学长度为63.5mm,采用一个衍射面的耦接镜设计实例。该设计结果适用于单丝直径16μm,截面直径6mm的光纤传像束。     

数码影像常用名词述语5——数码相机使用的镜头

焦距(focal length)无限远的物体经镜头成像,焦平面(CCD或CMOS)到镜头后主点的距离称为镜头的焦距值。当成像画幅尺寸一定时,焦距值越大,视场角越小;当物距不变时,焦距越长,像的尺寸也越大。(图1)     

网络摄像机制镜头的选型与技术应用

镜头的种类繁多，从焦距上分类．可分为短焦距、中焦距、和焦距和变焦距镜头；从视场的大小分类，可分为广角、标准、远摄镜头；ZK结构上分类，还可分为固定光圈定焦镜头、手动光圈定焦镜头、自动光圈定焦镜头、手动变焦镜头、自动光圈电动变焦镜头、电动三可变镜头（指光圈、焦距、聚焦这三者均可变）等类型。     

大视场自由曲面复眼设计研究

在大视场小体积的人造复眼结构中,倾斜的边缘子眼成像时存在较大的轴外像差。提出一种复眼结构,利用光线在子眼中的折转与自由曲面矫正像差,提高了边缘子眼的成像质量,进而增大了复眼结构的视场角。设计出5组子眼对180°视场成像,每组对应特定的视场范围。利用光学仿真软件CodeV对5组子眼分别做了光学仿真,得到了各组子眼的像差曲线,光学传递函数MTF曲线。结果表明,在整个180°视场范围内,频率为100 lp/mm时,MTF值均大于0.2,畸变在30%以内,复眼具有良好的成像质量。     

我用泽尼塔尔16mm F2.8鱼眼镜头

我是于2003年4月中旬向黑龙江省俄罗斯照相器材商店邮购了泽尼塔16mm鱼眼镜头的.众所周知,"鱼眼"镜头,就像鱼的眼睛,视角180°,其焦点距离极小.人们通常把视角范围接近或等于、大于180°的镜头称之为鱼眼镜头.鱼眼镜头有两种,一种是对角线鱼眼镜头,泽尼塔尔16mm镜头就属于对角线鱼眼镜头,它拍摄的影像能充满整张135底片;另一种则在胶片的影像形成一个圆圈之内,而不占满长方形范围,人们称之为非对角线鱼眼镜头.     

鱼眼显微镜光学

鱼眼镜头的视场角可以超过180度。它可以用作周视照相机镜头,也可以用作球幕电影的摄影和放映镜头。鱼眼显微镜光学是利用鱼眼镜头视场为180度,对有限远物体成象,与摄象机配套,可以把圆筒360度内壁上的物体,例如裂缝疵病,演示在电视屏幕上,起检测作用。文中附有一个实例,列出了镜头的结构参数,以及计算机输出的各种象差数据和相应的象差曲线图形。     

检测123：3只美能达α系列镜头测试简评（下）

３．２美能达ＡＦ８５ｍｍ ｆ／１．４Ｇ 这款镜头镜头号为：２０８０１１９１。最大光圈Ｆ１．４,采用浮动对焦设计,圆形９瓣光圈叶片,有特宽的橡胶对焦环、焦点固定按钮。 主要性能规格 焦距：８５ｍｍ光圈范围： Ｆ１．４至Ｆ２２镜头组成： ６组７片视场角： ２８°３０’最短摄影距离： ０．８５ｍ最大摄影倍率： ０．１２８滤镜尺寸： ７２ｍｍ外形尺寸： ７８ｍｍ（最长）× ７２． ５ｍｍ（直径）重量： ５５０ｇ 焦距实测值为８５．７５ｍｍ。与标称值的相对误差为０．９％。 摄影分辨率测试条件同上,该款镜头的分辨率如表２。…     

Design study of an infrared panoramic optical system

A design study was undertaken on an infrared, 3-5-μm, panoramic optical system for a particular monitoring application. The different types of systems investigated covered the conventional fish-eye lens system, a panoramic block arrangement, and a new type of configuration based on a panoramic shell. Examples of these systems are included, and their advantages and disadvantages are discussed.     

Optimization method for ultra-wide-angle and panoramic optical systems

To an ultra-wide-angle and panoramic optical system, the aberrations of point object at any field angle are separated into two types: the aperture-ray aberrations of off-axis point object and the chief-ray aberrations. A simple form of the triangular formulae of tracing an oblique-incidence ray is derived to calculate the chief-ray parameters and their aberrations; moreover, the aperture-ray aberrations of an off-axis point object are analyzed with the plane-symmetric aberration theory. Based on the two types of aberrations, we present a merit function for ultra-wide-angle and panoramic optical systems; the optimization program with the differential-evolution algorithm is then developed. To validate the optimization method we finally optimize a fish-eye lens and a catadioptric omnidirectional imaging system.     

LCD组件检测中用MTF评估自动聚焦分辨率的方法

液晶检测设备在自动聚焦后由于焦距变化,成像分辨率也不可避免的发生变化,为此必须提供一种快速评估检测设备实际分辨率的方法。由于检测设备总分辨率为镜头分辨率与相机分辨率的乘积,因此论文提出先根据相机的各种噪声模型建立相机对比度分辨值,接着用频率渐变的LCD黑白样条光栅评估不同频率下镜头MTF的像质退化情况,最后通过分析分辨率与对比度关系,得出相机最高对比度下能够分辨出的经过成像系统像质退化产生亮暗模糊所对应的空间截止频率。实验表明在使用光学检测设备对手机背光源进行缺陷检测时,论文的方法评估实际分辨率>17μm,用背光源标定样品实际检测后可以得到,对于17μm以上缺陷检测设备都能清晰成像,因此结果证明了该方法的有效性。     

Folded catadioptric panoramic lens with an equidistance projection scheme

A new formula for a catadioptric panoramic lens with an equidistance projection scheme has been derived. The fabricated lens has a field of view that is wider than that of any previously reported panoramic lens, and the nonimaged region near the back of the camera has a constant volume with zero angular extension.     

Panoramic lens

An infrared panoramic lens system that utilizes two lens groups to project a full 3600 cylindrical field of view onto a two-dimensional annular format is described. Each lens group has its well-defined role. The first group is a lens block that converts a cylindrical field of view into a two-dimensional annular format located within the lens itself, and the second group relays this image to some accessible location downstream from the optical system.     

Achromatic hybrid refractive-diffractive lens with extended depth of focus

A method for designing achromatic hybrid refractive-diffractive elements that can produce beams with long focal depths while they preserve the entire aperture for capture of light and high transverse resolution is presented. Its working principle is based on the combination of a diffractive optical element that generates a long range of pseudonondiffractive rays and a refractive lens of opposite dispersion to form an achromatic hybrid lens. A hybrid lens with a fast f-number (f/1) that works in the entire visible wave band (400-700 nm) was designed and fabricated. Simulation results demonstrate a factor-of-10 improvement in depth of focus compared with that of a conventional f/1 lens, with matching 1-microm lateral resolution. Experimental results confirm the effectiveness of the proposed method through demonstration of an achromatic hybrid lens with better than a factor-of-7 improvement in depth of focus and 1-microm transverse resolution.     

Zoom lens design for a novel imaging spectrometer that controls spatial and spectral resolution individually

A novel imaging spectrometer can individually control spatial and spectral resolution by using zoom lenses as the foreoptics of the system and a focusing lens. By varying the focal length we can use the focusing lens to change the spatial and spectral dimensions; with the foreoptics, however, we can change only the spatial dimension. Therefore the spectral resolution and the spectral range are affected by the zoom ratio of the focusing lens, whereas the spatial resolution and the field of view are affected by the multiplication of the zoom ratios of the foreoptics and the focusing lens. By properly combining two zoom ratios, we can control the spectral resolution with a fixed spatial resolution or the spatial resolution with a fixed spectral resolution. For an imaging spectrometer with this novel zooming function, we used the lens module method and third-order aberration theory to design an initial four-group zoom system with an external entrance pupil for the focusing lens. Furthermore, using the optical design software CODE V, we obtained an optimized zoom lens with a focal-length range of 50 to 150 mm. Finally, the zoom system with its transmission grating in the Littrow configuration performs satisfactorily as the focusing lens of an imaging spectrometer in the wavelength range 450-900 nm.     

High focal depth with a quasi-bifocus birefringent lens

The Strehl definition along the axis of a birefringent lens sandwiched between two polarizers is studied analytically. The optic axis of the birefringent lens made of a uniaxial crystal is perpendicular to the lens axis, and the system behaves like a bifocus lens for proper orientation of the polarizers. The Sparrow criterion is employed for designing an imaging system with high depth of focus. It is shown that, when the two foci are separated by the Sparrow limit of resolution, the focal depth is maximum and the intensity point-spread function remains almost identical within this limit. The resolution according to the Rayleigh criterion in this zone is more than that of an ideal lens.     

应用经纬映射的鱼眼图像校正设计方法

为了消除鱼眼镜头带来的形变,该文提出了一种应用经纬映射的鱼眼图像校正设计方法,推导了消除变形的数学依据,总结出一种不需要任何标定数据,快速的纠正等角鱼眼变形的算法。使用经纬映射图像的校正方法,可以把扭曲的半球鱼眼图像投射为普通照片的四方形状,也即通过投射降低图像的扭曲程度,在视觉上基本达到实用要求。     

Dark field imaging of semicrystalline polymers by scanning transmission electron microscopy

Scanning transmission electron microscopy (STEM) has been suggested to have advantages over conventional transmission electron microscopy (CTEM) for the observation of diffraction contrast features and diffraction patterns from radiation sensitive crystalline polymers. Because of image intensification, control of illumination location and magnification independent focus, STEM operation for focusing, area selection and set up of optics permits a high yield of systematic data. Dark field (DF) imaging is most useful when employed in conjunction with scanning microarea diffraction. For convergent beam microdiffraction and efficient DF imaging of thin crystals the beam divergence should be less than 5×10^–3 radians. For single beam DF, the reflection of interest is selected by the intermediate lens aperture. Use of a STEM annular detector to collect more than one reflection results in increased DF image intensity and resolution. Use of the entire azimuthal range of a single powder pattern reflection permits examination of crystal texture — in particular, images produced by chain axis reflections show the detailed arrangements of lamellae.