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L 是场景平均照度
S 是ISO指数
K 是反射式测光表校正常数
代入等式右边，曝光值是：
这样计算出的实际EV值和你的光圈/快门/ISO组合产生的EV值：（计算公式如下).
- EV100计算公式
- 其中N是光圈（f值）；t是曝光时间（快门），单位秒。
至此电子模拟测光的全部逻辑就完成了.
为什么电子模拟测光给出的TTL EV值会有偏差呢。这个就是18%灰度的问题了。18%灰度的计算是在测量亮度(luminance)的时候会起作用。
可以参看这个文章计算了CCD传感器饱和度和18%反射率来计算图像亮度的公式：
docs/sensitivity_EI.html
传感器实际的亮度计算公式:
I = πTLobj ⁄ 4N 2 (2)
where
I is the illuminance at the Image (sensor) plane in lux,
T is the lens transmittance fraction, generally assumed to be 0.9,
Lobj is the luminance at the Object plane (test chart) in candelas per square meter,
N is the f-stop (aperture).
Lobj = (0.18 ⁄ 1.414) Lsat = 0.1273 Lsat
1.414=141.4%值传感器可以包容的极限反射率大概是超过90%的纯白物体的反射。
传感器实际测得亮度同这个18%时候的标准基数相比就可以得出实际的物体反射的亮度了，然后带入公式计算得到EV值，然后再推算出 EV参数设置。
而ISO的定义公式为:来自柯达:
The Definition of EV
EV is defined mathematically as follows:
In the above formula, Aperture is the x.y in Fx.y, and Shutter Speed is the shutter speed in second. Thus, F4.0 and shutter speed 1/2 second yields EV=log2(42/(1/2))=5, and aperture F2.8 and shutter speed 1/4 second also yields an EV of 5. This means that the combination of aperture F4.0 and shutter speed 1/2 second and the combination of aperture F2.8 and shutter speed 1/4 second have the same exposure value and lie on the same EV line. Thus, in terms of a good exposure, the combination of F4.0 and 1/2 second is equal to the combination of F2.8 and 1/4 second!
~shene/DigiCam/User-Guide/4500/EXPOSURE/EV-overview.html
Phil在这本书的前言部分写到了黑白照片，“对我来说，黑白照片更有深度，它给了照片更柔和、更深层次的质感。那些灰色和阴影给照片带来了真正的活力。”你能解释一下这种观念，以及你是怎么做到的么？
Berstein：当你把 照片中的颜色去掉只留下黑白两色时，颜色的视觉冲击就不再重要，人们会更多的关注照片中所包含的情感。并不是说有颜色不好，我99%的时间并不是在拍黑白 照片，而是当你用黑白照相机记录下通常是彩色的世界时，比如比赛或者训练等等内容，那就会有一种真正的记录片似的的感觉。
分别代表卡尔·蔡司(Carl-Zeiss)镜头给各个数码单反厂家贴牌。
| ZA |
Zeiss for A-mount |
Zeiss lenses made for the Minolta/Sony A-mount. Available as top-end lenses for Minolta and Sony DSLRs (and some film SLRs).
|
| ZF |
Zeiss for F-mount |
Zeiss lenses made for the Nikon F-mount. These manual-focus only lenses are ultra-high quality and are generally considered to be some of the best made.
|
| ZK |
Zeiss for K-mount |
Zeiss lenses made for the Pentax K-mount. These manual-focus only lenses are the same ultra-high quality as the other mounts.
|
| ZM |
Zeiss for Ikon |
Zeiss lenses made for the Zeiss Ikon rangefinder camera.
|
| ZS |
Zeiss for M-42 Screw-mount |
Zeiss lenses made for older M-42 screw-mount cameras. These manual-focus only lenses are not only used for older film cameras, but can be fitted with adapters to work on many newer cameras..
|
| ZV |
Zeiss for Hasselblad |
Zeiss lenses made for the Hasselblad medium-format cameras. These manual-focus only lenses are used where critical sharpness is needed for the larger film format and now, larger digital sensors.
|