ISO Sensitivity

What is ISO?

ISO is a measurement of the camera's ability to capture light. The ISO number is directly proportional to the sensitivity of the camera towards light. Which mean, if we only adjust the ISO and fix the aperture and shutter speed, we can get bright or dark photos. Higher ISO number will give brighter image while lower ISO number otherwise. Raising the ISO helps to capture image in low light environment without the help of flash. However, high ISO sensitivity will add "noise" to your photograph making them seem grainy. 

Canon 600D @ 18mm, f/9, 1/25 sec, ISO-100

Canon 600D @ 18mm, f/9, 1/25 sec, ISO-400

Canon 600D @ 18mm, f/9, 1/25 sec, ISO-1600

Below are the photos that show the relationship between ISO and "noise": 

Canon 600D @ 18mm, f/9, 1/20 sec, ISO-100

Canon 600D @ 18mm, f/9, 1/40 sec, ISO-200

Canon 600D @ 18mm, f/9, 1/80 sec, ISO-400

Canon 600D @ 18mm, f/9, 1/160 sec, ISO-800

Canon 600D @ 18mm, f/9, 1/320 sec, ISO-1600

Canon 600D @ 18mm, f/9, 1/640 sec, ISO-3200

Canon 600D @ 18mm, f/9, 1/1250 sec, ISO-6400

Canon 600D @ 18mm, f/9, 1/2500 sec, ISO-12800

All the photos were taken with fix aperture of f/9 and increasing ISO. To get the proper exposure, the camera automatically adjust the shutter speed. Take a closer look at the door in all the photos, the "noise" is visible in the photos of ISO-3200 to ISO-12800. All cameras have different sensitivity to light, so it is advisable to understand your camera maximum ISO to avoid adding grains to your photo.