7.9: Gain and ISO

Gain

Gain is an amplification of the electrical signal sent from the image sensor, which is measured in decibels (db.). Although the image will appear brighter, the image quality will be reduced. This means the more gain you use, the grainier and lower-quality your image becomes. To preserve image quality, gain should not be used unless it is unavoidable like shooting a performance in a bar at night with no way to add lights. On the viewfinder, you will see the indicator for gain near the f-stop. If there is an “A” highlighted next to numbers measured in db, then auto gain is on. Make sure the gain is off.

ISO

This function is a bit different for DSLR/mirrorless cameras. On these cameras, there is a setting for ISO. ISO (International Organization for Standardization) refers to the sensitivity of film to light. Since moving to digital sensors, it now refers to the boost in the signal received by the image sensor. Some interpret this to mean it makes the image sensor more sensitive to light, but in reality, it is boosting the image signal to make the image brighter.

In digital cameras, gain and ISO are very similar in that they are boosts to image signals to make the image appear brighter. They differ in how they are measured. Gain is measured in db., ISO is its own measurement, usually measured in numbers ranging from 100 to 6400. ISO is linear in that ISO 200 is twice as bright as ISO 100. ISO 3200 is half as bright as ISO 6400. The higher the ISO, though, the more graininess you will see in the image.

The video below will demonstrate how ISO works using examples at different ISO levels.

To watch this video with closed captions: https://amara.org/en/videos/yuPAi3pJUn4k/info/what-is-iso-video-production-training/