Which aspect of photography does 'ISO' influence the most?

ISO is a critical setting in photography that determines the camera's sensitivity to light. When you increase the ISO setting, you effectively make the sensor more responsive to light, allowing for better performance in low-light conditions. This means that at higher ISO values, you can achieve a correctly exposed image with less light reaching the sensor, which is particularly useful in situations where the lighting is not ideal.

For instance, in a dimly lit environment, using a higher ISO can help you capture images without needing slower shutter speeds or wider apertures, which could introduce motion blur or a shallow depth of field, respectively. However, it's also important to understand that increasing ISO can contribute to a rise in digital noise in the final image, particularly at very high settings.

Understanding this aspect allows photographers to make informed decisions on exposure settings that achieve their creative vision while balancing image quality.