How “ISO” plays a role in exposure

In film (analog) photography, ISO is referred to as film speed which is actually the sensitivity of the film to light based on a scale created in 1987 by the International Organization for Standardization.

With digital technology the ISO setting on the camera controls the amplification of the image sensor which simulates the sensors sensitivity to light.

Digital sensors set to higher ISO values experience similar limitations as with film, where the noise in the image will increase as the ISO is increased. Digital noise is not as uniform nor as pleasing as film grain, however, software in the camera and in post-processing applications have improved to better control/reduce the digital noise.

©Trevor Awalt_MG_6570

f/8, 1/400, ISO 1000, @ 400mm

The digital noise in the resulting photograph depends on a number of factors, the age and type of camera sensor (technology), the processing engine of your camera, the ISO setting and the exposure. Notice with the image of the duck even though taken at an ISO of 1000 the resulting image is still of good quality.

We have learned so far that “aperturecontrols the amount of light into the camera and “shutter speedcontrols the amount of time the light is available to the sensor are the two controls to determine exposure. The third and final control for exposure is the “ISO” setting which controls the simulated sensitivity of the sensor to light. The ISO setting can affect the quality of your image in relation to digital noise, the lower the setting the less noise verses the higher the setting the more noise.

To find out how to set the ISO setting on your camera, refer to a previous lesson How to set your Camera’s; Aperture, Shutter Speed, and ISO.

©Trevor Awalt_ISO Setting Examples

Depending on the mode you have selected or the type of camera, you can control the ISO setting in full stops, typical values shown in bold, or 1/3 stop increments.

Now that we have learned all three controls, aperture, shutter speed and ISO as well as the creativity aspects of each, we now have the knowledge to discuss exposure in our next lesson.

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