Triangle Simplified – ISO

In digital photography, there are many settings that should be adjusted before each shot so that the best possible quality can be obtained.  We will explain them one at a time in this next series of posts.

In the exposure triangle, your first adjustment should always be your ISO adjustment.  What does ISO mean?  Quite simply, ISO stands for the International Organisation for Standardization and refers to how sensitive the sensor is to light.  Years ago, when photography was using film cameras, you needed to buy film based on the speed of the film (or ISO) and what you were planning to use it for; ie. ISO 200 was used for most images that would be taken outdoors and ISO 800 was meant for indoor or low light use. Photographers would have to change their film if the situation called for a different film speed (ISO) such as if he was taking pictures outside then had to move inside for more shots. With a digital camera, changing film is not necessary anymore because we can now change “film speed” on the fly by changing the setting in the camera.

The range of ISO settings goes from least sensitive (ISO 100) to most sensitive (ISO 6400) and beyond depending on the camera.  The lowest ISO means that the image sensor doesn’t need as much light to capture the image as ISO 6400 would need so most properly lighted situations can use ISO 100 and poorly lit situations would need a higher ISO like ISO 3200 or ISO 6400.

For the best quality images, you should choose the lowest ISO that you can for the situation.  For outdoor shots in the bright daylight, ISO 100-200 should be used most of the time however if indoors or at an event that does not allow flash, you may need a higher ISO to get the shot.  Higher ISO’s are more sensitive to light and can help capture images in low light situations but higher ISO’s can come at a cost in the quality of the image as you can see in the images below.

ISO 100
ISO 100
ISO 6400
ISO 6400

If you click on the images above, you will see the difference in quality of using different ISO settings.  Both images were taken using the same aperture but different speeds to accomplish a correct exposure.  There was no editing of the images except for a crop.

The image taken at ISO 100 has smooth lines and gradients whereas the image taken at ISO 6400 has quite a bit of granularity or “noise” that in most cases is undesirable.  There are times, though, that some noise is desirable and can be accomplished with adjusting the ISO to a faster speed such as ISO 3200.  It is a creative decision in this case and can also be accomplished with editing software such as Photoshop.

If you are not sure what ISO to use you can set the ISO to auto and the camera will choose the lowest ISO it can for the images you are trying to make.  You can use this as a learning tool if you examine the EXIF data on your images to see what ISO was chosen.  To see exif data, right click your image on your computer and go to properties.  On the details tab, you will find all the data regarding that image, including ISO, aperture, and shutter speed used to take the picture.

In our next post, we will jump into shutter speeds and how they affect your images.

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