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Monday, 01 January 2018 14:46

ISO Scale

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In analogue photography with ISO it was indicated the sensitivity to light of the films. The higher the ISO according to the ISO / ASA scale the greater the sensitivity of the film. A more sensitive film allowed to have a faster shutter at the same light. In particular, if with ISO 100 we could shoot in 1/50 of a second, with the same light and aperture, with a 200 ISO film you can use a double speed (1/125). This allowed to have sharper photography because less moves even if more grainy. Even in digital photography, sensitivity is expressed with the ISO scale derived from analog photography. The set ISO speed expresses the sensitivity of the sensor. As in analogue, even in digital photography, doubling the ISO set halves the time required to impress the sensor with the light required for the same aperture. Analogous to the digital ancestors, however, increasing the ISO too much can lead to inconveniences, while in the analogical one the ginning of the image increased, in the digital it increases the noise of the photograph. The advantage over analogue is that between one photo and another you can choose different ISO, while with the analog it was necessary to change the roll. The photographic noise also depends on the type of sensor mounted on our camera With high-density pixel CCD sensors adopted on current digital compact cameras, you will rarely get good results going over the ISO 800 value and so happens with medium digital cameras format. Things change, however, with the latest digital cameras APS format and Full Frame 24x36mm where you can get to use high ISO values. As mentioned above the ISO sensitivity can be an indispensable tool to make our photos clear. Increasing the ISO on a digital machine means that the signal created by the light striking the sensor is amplified, but at the same time noise is amplified at the same time. It is advantageous to increase the ISO settings of the camera in low light situations, such as interiors or exteriors in dark or very cloudy sky. In circumstances where the flash or tripod can not be used, ISO values ​​should be increased for faster shutter speeds. With slow shutter speeds there is a risk that the camera will move slightly while taking the picture, resulting in a blurred effect, or it may happen that the subject moves during the exposure, resulting in a blurred image. Unfortunately, as introduced above, using high ISO values ​​has disadvantages. In digital photography, increasing the ISO amplifies the electronic signal of the sensor, but it will also amplify the background electronic noise present in the circuits of the camera, thus causing interference that distorts the image signal and generates a dotted image or " noisy ", rarely beautiful to see.

The ISO scale is formed in such a way that doubling the numerical value doubles the sensitivity of the sensor to light. For example, if you double from ISO 100 to ISO 200 to get the same exposure you will have to set a half shutter speed (twice as fast). Every time you double the ISO value using the scale for Stop: 100, 200, 400,800, 1600, etc. the exposure is increased by an entire STOP. Using a higher ISO value can allow you to use a smaller aperture, and achieve greater depth of field, and make the most of the resolution of the lens. If you use a tripod in low light environments it is better to use low ISOs like 100 ISO, as well as when using the flash. The smaller the sensor size of the digital camera the lower the "noise" will be. The larger the sensor size the more light captures and as a result the signal will not need amplification which means less "less noise". Doubling the ISO sensitivity value the digital camera will be twice as sensitive to light and two times faster. There is a direct relationship between shutter speed and ISO settings. By increasing the ISO value, the shutter speed increases proportionally. For example, from 1/15 sec to 50 Iso, the shutter speed increases to 1/30 sec at ISO 100, 1/60 sec at ISO 200, 1/250 sec at 400 ISO. ISO Auto Many cameras have the option of auto ISO. When selected, the camera will monitor the shutter speed and if the time falls below the point where camera shake may occur (usually around 1/30 sec), the ISO value will automatically increase. This will help you avoid taking blurred images, but it can also introduce noise. Remember that manually it is preferable to use low ISO if you use a tripod, as there is no risk of vibrations and no noise will be produced in the images.



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