What should I consider when choosing ISO sensitivity?

Sensitivity refers to the sensitivity of the photosensitive element of a digital camera to light, which is abbreviated as ISO in English. The sensitivity values of digital cameras are generally 100, 200, 400, 800, 1600, etc. The larger the ISO value, the more sensitive the camera is, and the higher shutter speed can be used for the same exposure effect.

Influence of light sensitivity on exposure

As one of the three elements to control exposure, the sensitivity and sharpness of photosensitive elements to light will double with each increase of sensitivity, that is, the exposure will double; On the contrary, every step of decreasing sensitivity reduces exposure by half.

More intuitively, the change of sensitivity directly affects the setting of aperture or shutter speed. Take the exposure combinations of F2.8, 1/200s and ISO400 as examples. If you want to change the shutter speed and keep the aperture value unchanged, you can double the shutter speed (to 1/400) by increasing or decreasing the sensitivity. If you want to change the aperture value and keep the shutter speed unchanged, you can also set the sensitivity value. For example, if you want to increase the aperture by two steps (to F 1.4), you can reduce the iso sensitivity value by two steps (to ISO 100).

Influence of Sensitivity on Image Quality

In the case of sufficient light, try to use low sensitivity, because the photos taken with low sensitivity are more delicate. In the case of weak light, you can choose higher sensitivity to achieve full exposure, but this is at the expense of imaging quality, because too high sensitivity will produce obvious noise.

It should be noted that under the same sensitivity, the adequacy of light will also affect the amount of noise generated. For example, if you still use ISO400 sensitivity, it is not easy to see noise when shooting in clear daytime. Anyway, if you shoot at night, it's easy to see obvious noise. It should be noted that high-sensitivity cameras are not prone to noise. Some high-end digital cameras have no obvious noise even if they are set to ISO6400, while some high-sensitivity cameras, such as some entry-level cameras, have obvious noise.

Principles of setting sensitivity

As we all know, increasing the sensitivity can appropriately increase the shutter speed or reduce the aperture of the first stop, while setting the sensitivity too high will produce noise and affect the image quality, so photographers should master certain principles when setting the sensitivity.

1. If light conditions permit, it is best to take photos with low ISO sensitivity to ensure higher image quality and better detail performance. If you must use high sensitivity, low-end digital SLR cameras should not exceed ISO800, and high-end cameras should not exceed ISO 1600.

2. In dark conditions, if low sensitivity can be used, it is best to shoot with a tripod. If it is hand-held shooting, in order to ensure clear imaging, the sensitivity can be appropriately improved, but at the same time, the loss of image quality caused by high sensitivity should be weighed and considered.

3. The sensitivity should be set according to the different themes and uses of photos. For news photography and sports photography, because there is usually no need to enlarge photos in a large area, you can choose higher sensitivity to make up for the underexposure caused by high-speed shutter, such as using ISO400- 1600. For commercial photography, because of the high quality requirements, photos are often enlarged, so it is best not to use too high sensitivity, and often use ISO 100-200.