In photography, ISO is a measure of how sensitive a piece of film or digital sensor is to light—the higher the ISO the more sensitive. With a low ISO you need to use a longer shutter speed or a wider aperture than you would if you’re using a high ISO. Most digital cameras have an ISO range of between around 100 and about 12,800.

在摄影中，ISO可以衡量胶片或数字传感器对光线的敏感程度-ISO越高，感光度就越高。 与较低的ISO相比，与较高的ISO相比，您需要使用更长的快门速度或更大的光圈 。 大多数数码相机的ISO范围在100到12800之间。

The name ISO comes from the body that designated the standard: the International Organization for Standardization (yes, the acronym should be IOS but whatever). This means that all camera manufacturers calibrate their sensors to roughly the same values. ISO 100 on a Canon 5D MKIV should have the same sensitivity to light as ISO 100 on your iPhone.

ISO名称来自于指定标准的机构：国际标准化组织(是的，首字母缩写应为IOS，但无论如何)。 这意味着所有相机制造商都将其传感器校准到大致相同的值。 佳能5D MKIV上的ISO 100对光的敏感度应与iPhone上的ISO 100相同。

ISO如何运作 (How ISO Works)

Although they measure the same thing, ISO works a bit differently for film and digital cameras. For film, it’s a measure of how quickly the chemicals used react to light. The quicker the chemicals react, the higher the ISO value and the less light that’s needed to take a photo. We’re going to focus more on digital cameras here, though.

尽管它们测量的是相同的东西，但ISO对于胶卷相机和数码相机的工作方式却有所不同。 对于电影来说，它是衡量所用化学物质对光React的速度的度量。 化学物质React越快，ISO值就越高，拍照所需的光线就越少。 不过，我们将在这里更多地关注数码相机。

Every digital sensor is made up of millions of smaller sensors. A 20 megapixel sensor, for example, has 20 million small sensors: one for each pixel. When photons of light hit each of these tiny sensors, an electric charge is generated. The more photons that hit each sensor, the stronger the charge. The value of the charge at each sensor is what your camera uses to determine how bright or dark the corresponding pixel is in your image.

每个数字传感器均由数百万个较小的传感器组成。 例如，一个20兆像素的传感器有2000万个小型传感器：每个像素一个。 当光子撞击这些微型传感器中的每一个时，都会产生电荷。 撞击每个传感器的光子越多，电荷越强。 每个传感器上的电荷值就是您的相机用来确定图像中相应像素的亮度是多少。

The relationship between the charge detected by the camera and the brightness of each pixel is essentially arbitrary. The sensors are calibrated so that an image shot at ISO 100 on a digital camera would appear about the same as an image shot on ISO 100 film.

照相机检测到的电荷与每个像素的亮度之间的关系基本上是任意的。 对传感器进行校准，以使在数码相机上以ISO 100拍摄的图像看起来与在ISO 100胶片上拍摄的图像大致相同。

While ISO 200 film is chemically different to ISO 100 film, a digital camera always uses the same sensor; this means it’s always getting the same electric charge. Instead, ISO values are emulated through amplification. When you turn your camera’s ISO up from 100 to 200, nothing changes with the sensor; the value of the charge the sensor detects (and the corresponding brightness of the pixels) is just doubled as you take the image. This is why digital cameras are so much better in low light than film cameras.

尽管ISO 200胶卷在化学上与ISO 100胶卷不同，但数码相机始终使用相同的传感器。 这意味着它总是获得相同的电荷。 而是通过放大来模拟ISO值。 当您将相机的ISO从100提高到200时，传感器不会发生任何变化。 拍摄图像时，传感器检测到的电荷值(以及相应的像素亮度)只是增加了一倍。 这就是为什么数码相机在低光下比胶卷相机好得多的原因。

如何测量ISO (How ISO is Measured)

ISO is measured using a simple logarithmic scale. Every time you double the ISO value, the brightness of the image increases by one stop.

ISO使用简单的对数刻度进行测量。 每次将ISO值加倍，图像的亮度就会增加一档 。

This means that the difference in brightness between an image shot at ISO 100 and ISO 200 is the same as the difference in brightness between an image shot at ISO 800 and ISO 1600. On your camera, ISO 6400 is six stops brighter than ISO 100, not 64 stops brighter.

这意味着以ISO 100和ISO 200拍摄的图像之间的亮度差异与以ISO 800和ISO 1600拍摄的图像之间的亮度差异相同。在您的相机上，ISO 6400比ISO 100高6级，没有64会变亮。

您应该使用什么ISO？ (What ISO Should You Use?)

Along with shutter speed and aperture, ISO is one of the pillars of digital photography. While it might not affect the look of your images as much as the other two factors, it’s still important to know what value to select for different situations. Check out our guide to your camera’s most important settings, including ISO, to learn more about how these settings work together.

除了快门速度和光圈外，ISO也是数码摄影的Struts之一。 尽管它可能不会像其他两个因素那样影响图像的外观，但了解针对不同情况选择什么值仍然很重要。 请查看有关相机最重要设置 (包括ISO)的指南，以了解有关这些设置如何协同工作的更多信息。

翻译自: https://www.howtogeek.com/302755/what-is-your-cameras-iso-setting/