How to choose ISO correctly in photography?

Friends who have bought camera film must have noticed the words ISO 100, ISO200 and ISO400 on the film package. The ISO value indicates the sensitivity of the film. According to the chemical reaction speed of film to light, we divide film into slow film and high speed film. The International Organization for Standardization (ISO) has formulated the standard of film photosensitive speed, which is determined as ISO 100, ISO 200...ISO The higher the ISO value, the faster the film photosensitive speed. Fast exposure speed means that you can use higher shutter speed to get the same exposure effect in the same situation. ISO 100 is twice as fast as ISO50. For example, under the same conditions, it takes1125 seconds to use ISO50, and only takes 1/250 seconds to switch to ISO 100 film.

■ ISO for digital cameras

Now we know that sensitivity is marked by ISO value, and high ISO value represents faster sensitivity. Digital cameras also imitate traditional film, and set ISO value to express sensitivity. However, changing the sensitivity of a digital camera does not require changing the film, just adjusting the ISO value. The photosensitive element of a digital camera is constant, and it uses the method of treating several pixels as 1 pixel, thus improving the photosensitive speed. For example, the common ISO 100 is sensitive to every pixel of the photosensitive element. To improve the sensitivity to ISO400, you only need to treat four points as 1 point, and you can get four times the sensitivity.

■ The influence of ■ISO on shooting

The influence of ISO on shooting is manifested in two aspects: one is speed, and higher sensitivity can get faster shutter speed and be easier to understand. The second is image quality. The lower the sensitivity, the finer the image quality, the higher the sensitivity and the higher the noise.

■ How to use ISO

We can consider how to choose the appropriate sensitivity from the above two points.

Requirements for image quality

When shooting many works, fine picture quality is almost an important factor to determine a good work. Such as shooting scenes, portraits, landscapes, etc. At this time, we can choose low sensitivity to shoot.

Shutter speed requirements

You can increase the shutter speed by increasing the aperture, increasing the light, using a flash, etc. Using a tripod also allows us to get stable shooting at a slow shutter speed. However, when the above conditions are not met, we can also consider increasing the ISO value of the digital camera to increase the shutter speed, so as to avoid blurred images due to jitter in low light.