ISO
ISO 在数码相机时代指计算放大照片亮度的程度。ISO 主要功能就是通过芯片计算让照片更亮，但更高的 ISO 同时会导致成像质量下降。
当 光圈 和 快门 时间固定后，到达相机传感器的光通亮是一定的，我们称这些光为信号（Signal）。ISO 负责将信号“人工”放大，以提高成像亮度。但提高 ISO 同时也会造成数字噪音也被放大，最终造成成像质量降低。
ISO 全称是“International Organization of Standardization”，历史上相机制造商需要让电影相机遵守的传感器感光度标准。
但现在数码相机时代，相机不再遵守该标准。ISO 也和传感器感光度没有任何关系。
基础 ISO
相机自身的最小原始 ISO（the lowest native ISO） 也叫基础 ISO（base ISO）。基础 ISO 的成像质量最好，一般而言，尽可能使用基础 ISO。
ISO in photography can be explained as a way to increase the light information captured by the camera sensor.[1]
The important thing before diving deeper is to eliminate two misconceptions:
- Historically, ISO in photography comes from the acronym “International Organization of Standardization” and a time when camera manufacturers needed to homogenize the sensitivity ratios in film cameras. Today, ISO in digital cameras doesn’t follow the standards of the ISO organization.
- Despite what many people still think, ISO in digital photography has nothing to do with increasing the light sensitivity in the camera sensor. However, there are still photographers who wrongly refer to this term as ISO Sensitivity in digital photography.
The main effect of ISO in photography is to “artificially” increase the light captured by the camera sensor, resulting in a brighter final image.[1:1]
In simple terms, ISO in photography works the following way:
- The camera sensor collects an amount of light that depends on the aperture of the lens and the time that the sensor is exposed (shutter speed). This light information is also known as “Signal” in photography.
- When this light (or signal) is received, ISO plays a role in making an interpretation of it. This interpretation is related to the amplification of this light.
- When ISO amplifies this signal/light, the final image will be brighter, but it will progressively start generating more digital noise as you increase the ISO, compromising the final quality of the image.
The lowest native ISO on your camera is your “base ISO”. This is a very important setting, because it gives you the potential to produce the highest image quality, minimizing the visibility of noise as much as possible. Some older DSLRs and a number of modern cameras, such as the Fuji X-T2 have a base ISO of 200, whereas most modern digital cameras have a base ISO of 100. Optimally, you should always try to stick to the base ISO to get the highest image quality. However, it is not always possible to do so, especially when working in low-light conditions.[2]