Lesson 7: ISO

ISODigital cameras have an ISO rating indicating their level of sensitivity to light. The normal setting for most cameras is ISO 100, although some go as low as ISO 50. The sensitivities can be increased to 200, 400, 800, or even 3,200. High-end digital SLRs also allow some intermediary values. When increasing the sensitivity, the output of the sensor is amplified, so less light is needed. Unfortunately the undesired noise is also amplified. This creates more grainy pictures, just like in conventional photography, but because of different reasons. It is like you will turn up the volume of a radio with bad reception. This will not only amplify the desired transmission but also the undesired noises. Lately a lot of improvements has been done in sensor technology to reduce the noise level at higher ISOs, especially on higher-end cameras.

Here is an example of how ISO level influence the final image:

ISO 100 and 1600

So your question may be: why should I use higher ISO level if it adds so much noise in the picture? The answer is very simple. A photography with some noise in it is preferred to a blurry one. When you press the button to take the picture, a mechanism in the camera opens and expose the sensor to light for an amount of time (it is called exposure time). The lower the light level is, the greater the exposure time will be. If you are taking the picture from your hand, a longer exposure (how long? this will discuss in further lessons) will result in a blurry picture because of the uncontrollable shake of hands or movement of subject. In this case, if you can’t control the level of light, the only thing you can do is to increase the sensibility of the sensor (higher ISO level) which will require less light for the picture so a lower exposure time.

In conclusion, the different ISO levels makes the cameras more versatile, allowing us to use them in different light conditions, but with the disadvantage of adding some noise into the final picture.

2 Responses to “Lesson 7: ISO”

  1. Ameena says:

    thank you .. great lesson

  2. Andrei says:

    I’m glad that it helped 🙂