如何应用数码相机的曝光弥补
 

图文：邢亚辉
模特：方澍、娟子、诗涵

一＼什么是曝光补偿
曝光补偿是一种曝光掌握方式，就是在通过机身对被摄体测光当前，得出的快门和光圈组合的参数，再通过曝光补 偿人为转变这一次测光得出的快门速度。加曝光补偿（加曝）则快门减慢，因为告知机器要获得更多的曝光，在光 圈不变的情况下，要增加通光的量，所以要减慢快门；反之，减曝则快门速度加快，相机根据测光调整所拍摄风物 的曝光量，但因为拍摄物体的亮度散布不均，可能会呈现，例如在晶莹的背景前拍人物的逆光照，而使人物曝光不 足的景象。这时可以用曝光补偿来解决这类问题，有曝光补偿的相机通常可以进行+2、+1、0、-1、-2等调整，如果主体曝光不足，则用正补偿，增加曝光量，反之使用负补偿，减少曝光量。
当我们使用手动档来拍摄，这个时候就没有曝光补偿的概念的了，polo ralph lauren wholesale，因为手动档的快门速度和光圈大小都是由我们设置的。只有当影响曝光量的两个参数(快门速度 & 光圈大小)中的任何一个是由相机的自动测光系统来决定的时候(ＡＶ机会根据自动测光的结果来决定快门速度， TV档时相机遇根据自动测光的结果来决定光圈大小，P档时相机会根据自动测光的结果来快门和光圈的组合)， 才会存在"曝光补偿"的概念。这个"曝光补偿"是让摄影师去根据实际的拍摄情形进行的主观调节(补偿)相机 的自动测光结果的。而M档时，相机已经不再参加快门或光圈的设置了，也就基本没有了"曝光补偿"的概念了， 这是我们要注意的。
二＼为什么要曝光补偿： 曝光补偿是补充相机拍摄人像时的自动测光不是最佳后果，或是摄影师主观认为不是最佳时，人为主观的对它进行 修改。
三＼人像摄影中哪些情况下需要曝光补偿？
1、拍摄人像的环境较阴暗，须要增加亮度，而不任何补光工具时，可以对主体人物曝光进行补偿，恰当增长曝光 量。进行曝光补偿的时候，如果照片过暗，要增加EV值，EV值每增加1.0，相称于摄入的光线量增加一倍， 假如照片过亮，要减小EV值，EV值每减小1.0，相称于摄入的光线量减小一倍。
2、当我们在白色背景环境中或人物衣着白色衣服拍摄时，在照片里看起来白色是灰色或不够白的时候，需要要增 加曝光量进行曝光补偿，这是因为相机在自动挡时的测光往往以核心的主体为着重，白色的主领会让相机误认为很 环境很明亮，因此曝光不足。
3、当咱们拍摄的画面中有大面积的深色或浅色区域，而人物的面部在画面中只占较小的比例，如按均匀测光所得 到的曝光值曝光，成果人物的面部不是曝光适度就是曝光不足。这时就要在平均测光的基本上做曝光 补偿。
4、当我们的拍摄人物与背景的光比太大，尤其逆光拍摄人像时，相机的自动测光有时也会做犯错误的反映，造成 曝光的失误。这时应用相机的自动测光，它可能是所摄目的的平均值，这样很可能拍摄出来的人物，背景正常然而 人的脸部变暗，这时就需要进行“曝光补偿”了，增加曝光量。
四＼人像照片增减曝光量示例
１＼曝光补偿量的单位是Ev。在曝光的时候，通常用快门速度(T)跟光圈值(f)的组合来表示，当初同一用 Exposure Value (EV，曝光值)来表现。EV是英语Exposure Values的缩写,是反应曝光多少的一个量，其最初定义为：当感光度为ISO 100、光圈系数为F1、曝光时间为1秒时，曝光量定义为0,曝光量减少一档(快门时光减少一半或者光圈缩 小一档),EV值增添1。
+2.0Ev=4倍 曝光量
+1.0Ev=2倍 曝光量
+0.0Ev=所盘算的 曝光量
-1.0Ev=1/2倍 曝光量
-2.0Ev=1/4倍 曝光量
２＼曝光补偿是数码相机模式拍摄状况下的曝光量微调，而且因模式的不同而浮现不一样的调剂方式 ：
　　Ａ＼在程序模式P档下，我们若调高EV请求增大曝光量，相机内部电子电路就会依据场景状态，自动决议或 是加大光圈，或是延伸快门时间。
　　Ｂ＼在光圈优先Av档下，增加EV象征着延长快门时间，减少EV就是缩短快门时间。
　　Ｃ＼在快门优先Tv档下，增加EV就相当于加大光圈，反之就是减小光圈。
　　Ｄ＼在全手动M档下，由于光圈和快门都由用户自行设定，曝光补偿就不存在了。
目前主流的数码相机的曝光补偿分档要更细一些，是以1/3EV为距离的，于是就有-2.0、-1.7、-1、-1.0、-0.7、-0.3和+0.3、+0.7、+1.0、+1.3、+1.7、+2.0等共12个级别的补偿值。
图1　在原测光基础上增加0.5EV曝光量（半挡），主体影调得到改良
图２　在原测光基础上增加1EV曝光量（1挡），主体得到正确表现
图３ 在原测光基础上增加2EV曝光量（2挡），主体曝光过度

用人像照片作减少曝光量示例
图4　在原测光基础减少0.5EV（半挡）曝光量，主体影调得到改善
图5　在原测光基础减少1EV（1挡）曝光量，主体得到准确表示
图6 在原测光基础减少2EV（2挡）曝光量，主体曝光不足

所以说，最终决定权仍是在我们的大脑，根据实际情况和主题需要，机动控制、灵巧应用是终极目标 。
五＼白加黑减”等使用曝光补偿的要领
曝光补偿的准则我们普通可以遵守“白加黑减”的法则。如果画面中有大片白色物体或者有灯等特殊亮堂的物体， 就要相应增加曝光量；如果取景框中有大片玄色的物体，则要减少曝光量。 正常来说，在光照比较平均的情况下相机的自动测光和曝光比较准确，但在明暗反差很大时自动曝光往往不准，所 以需要手动曝光补偿。
画面中白色占重要，测光系统会认为太亮，自动减低曝光值，因而要加。反之画面太暗，测光系统会以为太黑，自 动增加曝光值，所以要减。所以，所有相机的测光系统不是在任何情况下的测光都准确。
实践上说是“白加黑减”，但是在实际的拍摄中这并不都即是在光明的环境下就增加EV，黑暗的环境下就减少E V，我们应该根据实际情况来剖析决定。 在光线不平匀的场景下，如果测光范畴是高亮处（白处），相机就会以该处的测光值，作为整个场景亮度的旁边点 ，cheap ralph lauren polo shirts，造成整体欠曝画面偏暗，这时要适当调高EV（白加），增加曝光量，就可以让照片取得正确的曝光。相反，同 样是光线不平均的场景下，如果测光规模是昏暗处（黑处），相机也会以该处的数值作为全场景的亮度中点，于是 全部画面过曝显得很亮，只有调低EV（黑减），减少曝光量，才干拍出正常的照片。图7

六＼包围曝光（也称括弧曝光、阶梯式曝光）
曝光补偿除了手动设置外，我们还有更方便的方式，也可以由数码相机依照预设的EV值本人来实现，那就是“包 围式拍摄”， 包围式曝光是相机的一种高等功能。就是一次连拍三张或者连按三次快门。这三张中，第一张是正常曝光，第二张 是曝光不足，第三张是曝光过度（这个次序可以设置）。这样，这三张中，总有一张是适合的，从而保证总能有一 张合乎摄影者的曝光用意。。图8、图9、图10。在设置包围式拍摄时，先要设定一下EV的级差。就是这三张 的曝光量相差多少个EV？比方说.03。那么第二张拍摄的就是EV=-0.3，第三张拍摄的就是EV=+0.3。也可以设置为0.5或是1.0。这个措施比拟便利快捷。当然，这 里面毕竟级差应当是多少，还得凭一点儿教训。我们可以分几回来实验不同的级差的变更。包围式曝光个别使用于 静止或慢速挪动的拍摄对象，因为要持续拍摄多张，很难捕获动体的最佳拍摄机会。


七＼曝光记忆锁（AE锁、AEL）
有的照相机设有自动曝光锁定装置，用“AEL”来标记。AE是automatic exposure自动曝光节制安装的缩写，用于自动曝光时人为把持曝光量，保障主体曝光畸形。使用AE锁的 留神事项：1、手动方法或自拍时不能使用自动曝光(AE)锁。 2、按下主动曝光(AE)锁之后不要再调节光圈大小。 3、用闪光灯摄影时不要应用(AE)锁。用这种自动曝光锁定装置测光需走近被摄体，当被摄体测光精确之后， 按下AEL按钮，将测光读数锁定，再退回放原处进行构图对焦。这样，照相机的测光体系就不会受其余光芒的烦 扰，而得到正确的曝光，这时也能够不必曝光弥补。
八＼尼康的示例图
图1２尼康D700（或其他尼康单反）的
图1３曝光补偿、
图1４、其曝光补偿功能怎么调用，拍摄液晶屏画面
图1５包围曝光
图15-1-2-3其包围曝光功能怎么调用，拍摄液晶屏画面
图16曝光记忆锁在机身的位置

佳能的示例图
图1８佳能5D（或50D、40D）的
图1９曝光补偿、
图２０其曝光补偿功能怎么调用，cheap hollister clothes，拍摄液晶屏画面
图２1包围曝光
图２1-1其包抄曝光功效怎么调用，拍摄液晶屏画面
图２2曝光记忆锁在机身的地位
以上内容仅供参考！邢亚辉 2009 北京

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