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测光知多少 鲜为人知的7个测光知识

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  你会发现,相机的测光虽然越来越智能化,但还是有曝光错误的时候。到底相机的测光系统能不能做到在任何情况下都万无一失呢?答案可能是否定的。这与相机测光系统的局限性有关,今天就来说说关于测光,那些你可能没意识到的事,并告诉大家如何利用相机的各种测光模式拍出效果最佳的照片!

       相机不能分辨黑白

  很多人不知道,其实相机的测光系统根本分不清楚它的对象是一只黑猫还是一袭白衣。因为相机无法像人眼一样识别主体色彩。
  相机只是被设定为通过测量被摄对象反射回来的光亮度来调整曝光,最终在照片上产生中灰影调。而这个反光率为18%的中灰影调,是根据自然景物中间调(灰色调)的反光表现而定的。所以拍摄一只黑猫时,要减少1-2档曝光量,否则照片上得到的就是一只灰猫。而想真正还原白衣飘飘的场景,就得增加1-2档曝光。
  因此,当被摄体是黑色或白色时,曝光要遵循“白加黑减”的原则。

      评价测光(矩阵测光)不适用逆光

  评价测光(矩阵测光)模式是将取景画面分割成数个不同区域,将各个区域所测的曝光值经由机内的程序运算,求出最适合的光圈及快门组合。
  这种测光模式非常智能化,它能模拟人脑对拍摄时经常遇到的均匀或不均匀光照情况做出判断,但这种判断也会出现失误。
  评价测光(矩阵测光)在逆光环境下会误以为你想得到一个脸部曝光正确的背光人像,所以就按着猜测的那样曝光,因此最后出来的不是你想要的利落的剪影。

      中央重点测光是较有效的测光方式

  这也是几乎所有的相机生产厂商都将中央重点测光作为相机默认测光方式的原因。中央重点测光是一种传统的测光方式,它的测光算法较简单粗暴,主要重视画面中央约2/3的位置的测光数据,而画面中央以外的测光数据则不作主要考虑。
  对于有经验的摄影师,中央重点测光是一种较有效的测光方式,因为对他们来说这种方式测光比使用评价测光更加容易控制效果。

      某些相机测光有偏差

  如果你拍出来的照片一直存在曝光不足或曝光过度的问题,要不是使用不当,那就可能是相机本身的问题。
  例如宾得K20D就普遍存在欠曝问题,而尼康D800则收到大量过曝的反馈。面对这种情况,你需要掌握所使用相机的色彩以及曝光倾向,设置一个固定的曝光补偿来调整曝光误差。如果一直出现照片曝光不足,那么调高1-2EV试试。如果是经常性的曝光过度,就降低1-2EV,直到得到最佳的曝光效果。

      用点测光了解场景的动态范围

  点测光只对很小的区域准确测光,区域外景物的明暗对测光无影响,所以测光精度很高,适用晚会等场景。
  但点测光也可以用来大概了解场景的动态范围,首先每个场景都有明暗差异,点测光可以帮助我们测评整个场景的明暗差距,并预计最后曝光情况。
  使用快门优先模式,在曝光补偿为0的情况下,用中心点对着最亮的地方测光,假设得到的光圈是F11,再对着画面最暗地方测光,假设得到的光圈是F2.8,则我们能得出场景需要的宽容度是4个曝光级,在相机的正常曝光范围之内。但如果差值超过5EV,则需要考虑拍摄一系列不同曝光值的照片,然后进行后期合成。

       包围曝光是退而求其次的完美
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  无论什么场景,我们都想拥有完美的曝光,但由于种种原因,有时会很难选择适当的曝光补偿和白平衡设置,并且也没有时间在每次拍照后检查结果及调整设定。所以相机为我们提供了自动包围曝光功能。
  自动包围曝光会自动对被摄物体拍摄连续拍摄2、3或5张曝光量在0.3到2.0EV之间的照片,你可以在众多不同曝光的照片中选择一张最完美的。

      不同的取景方式导致不同的测光结果
8.jpg
  当你使用不同的取景方式时,相机的测光方式也会发生变化。取景器取景时,入射光线通过相机的镜头以及反光板折射,进入机身内置的测光感应器,这块测光感应器和CCD或者COMS的工作原理类似,将光信号转换为电子信号,再传递给相机的处理器运算,得到一个合适的光圈值和快门值。
  而实时取景时,由于光路设计不同,曝光结果是由感光元件测光并计算得出的。所以不同的取景方式会得到不同的测光结果,有时候差异高达0.3EV。

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我想境境  版主  发表于 2016-4-28 17:39:29 | 显示全部楼层

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我想境境  版主  发表于 2016-5-6 20:22:28 | 显示全部楼层

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小源  管理员  发表于 2016-12-8 10:31:57 | 显示全部楼层
某些相机测光有偏差

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张文  等待验证会员  发表于 2017-4-25 15:14:33 | 显示全部楼层

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张文  等待验证会员  发表于 2017-5-8 18:35:37 | 显示全部楼层

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bld7Ee4Q8  等待验证会员  发表于 2017-5-26 15:27:03 | 显示全部楼层

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   http://www.doarnews.com/forum.php?mod=viewthread&tid=1525711&pid=1548751&page=1&extra=page=1#pid1548751
  
   http://bbs.gulf-musical.com/forum.php?mod=viewthread&tid=347594&pid=356488&page=1&extra=page=1#pid356488
  
   http://www.jwg360.com/forum.php?mod=viewthread&tid=1546&pid=14391&page=309&extra=page=1#pid14391
  
   http://vanforfun.com/forum.php?mod=viewthread&tid=267403&pid=315960&page=1&extra=page=1#pid315960
  
   http://www.kanuge.com/forum.php?mod=viewthread&tid=60&pid=359030&page=8&extra=page=1#pid359030
  
   http://sfj88.com/forum.php?mod=viewthread&tid=8069&pid=49277&page=38&extra=page=1#pid49277
  
   http://www.doarnews.com/forum.php?mod=viewthread&tid=1525722&pid=1548745&page=1&extra=page=1#pid1548745
  
   http://vanforfun.com/forum.php?mod=viewthread&tid=267444&pid=315959&page=1&extra=page=1#pid315959
  
   http://www.upyymovie.com/forum.php?mod=viewthread&tid=29175&pid=539956&page=3&extra=page=1#pid539956
  
   http://www.girl91.com/forum.php?mod=viewthread&tid=1247&pid=680612&page=8&extra=page=1#pid680612
  
   http://www.kanuge.com/forum.php?mod=viewthread&tid=18&pid=359025&page=24&extra=page=1#pid359025
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