Adjust ISO in Digital Macro Photography - dummies

By Thomas Clark

In close-up and macro photography, ISO can be as important as aperture and shutter speed in determining the look of an image. A composition that requires a large aperture and a slow shutter speed lets in a lot more light than one that requires a small aperture and a fast shutter speed. Your camera’s ISO setting helps to provide the exposure you want in both of these scenarios.

ISO determines the sensitivity of your camera’s digital sensor. A low ISO (such as 50) causes the sensor to have a slower, but more reliable, reaction than a high ISO (such as 3200). Reliable, in this case, refers to the quality of the image it produces in comparison to the higher ISO.

Use a low ISO when a scene has adequate light based on your exposure settings. This produces an image with minimal digital noise (red, green, and blue specks found in digital images, similar to film grain). If a scene lacks adequate light for your exposure settings, you need a higher ISO. This produces an image with more visible digital noise.

As your camera’s sensor becomes more sensitive to light, it becomes more likely to pick up digital noise in the process. Noise appears mostly in an image’s shadow areas.

This figure shows the difference between an image taken with a low ISO (left) and one taken with a very high ISO (right). Notice how detail is lost in the darker areas in the image on the right, and how the color appears distorted. A high ISO can produce a proper exposure in lowlight situations, but comes at the cost of digital noise in your images.


100mm, 0.5 sec, f/11, 100    100mm, 1/60, f/8, 3200

Each of the three exposure settings on your camera has its own effect on the look of your images. Aperture determines depth of field, shutter speed determines how motion is depicted, and ISO determines the level of noise. Consider all three of these factors and choose the best combination of settings for a specific scene.