ISO Settings Explained

One of the most confusing topics for most beginners is the idea of ISO settings. People often wonder which ISO setting to use on their camera and how does it affect the photograph they are taking. This article will explain what the magical ISO is all about.

The History of ISO Settings

The ISO settings of a digital camera has a history from the days of film. In the old days, when everyone used film cameras for shooting pictures, different films were made using different chemicals and hence had different sensitivity to light. Some films were more sensitive to light and could give the same exposure even in dark conditions. These film were called fast film. Other films needed more light to fall on them to give the same exposure and were called slow films. Initially, there was no standard way of defining how fast or slow a film was. That’s when an ISO standard evolved. In many of the older automatic cameras, you had to set the ISO speed of the film manually so that the meter could adjust the shutter speed. Later, the cameras were able to read the film speed from the film itself.

How fast is ISO 100?

An ISO 100 speed film on a sunny day requires a shutter speed of 1/100th of a second at f/16 aperture to get the right exposure. A 200 speed film is twice as sensitive and hence only needs 1/200th of a second of exposure to get the same exposure at the same aperture. Similarly, at ISO 800, you only need 1/800th of a second at f/16 to get a proper exposure on a sunny day.

Why have different film speeds?

Different film have different properties. Faster films like ISO800 end up giving a grainer image, but they allow you shoot indoors or in the evenings without a flash. They are also very useful in sports photography where you want to freeze the action. If you don’t want the grainy pictures of a fast film, but still want to shoot indoors, one option is to use a tripod. However, this doesn’t work if your subject is moving as well.

Slower films are less grainy. They give a clearer picture. However, pictures taken with them in low light conditions might suffer from motion blur due to your hand shaking or the subject moving. They are used often in outdoor photography or studio photography where there is amble light. Slower films also help when you want to deliberately take a slow shutter speed shot like shooting a waterfall or creating blurs. You can read this post for more information on that.

Since both kind of film had their advantages and disadvantages, photographers using film had to often carry cameras loaded with different film speeds.

I have a Digital Camera, why are you telling me all this?

Well.. all that we talked about is actually applicable to digital cameras as well. Digital Sensors can be made more sensitive by artificially boosting the reading they give out. This makes the sensor more sensitive to light, but introduces noise or grain in the photograph. The same definition of ISO holds good for Digital Cameras as well. A 100 speed film needs 1/100th of a second shutter speed on a sunny day to give the right exposure. One of the best things about Digital Cameras is that you don’t have to wait to finish a film before switching ISO settings.

With digital cameras, as the sensor technology evolves, the amount of noise and graininess is decreasing. Newer cameras have very low noise and can often be used even at 800 or 1600 speed, if you don’t plan to take big prints. While buying a camera, remember that cameras with bigger sensors tend to have less noise at higher ISOs, so use that as a parameter to evaluate your camera. You should check the Camera’s perform in low light. Many sites give detailed reviews of high ISO performance. With image processing, one can also reduce the noise in post processing using filters.

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