Article By – Chinar Tekchandani & Apurv Jadhav

When one hears the term ISO, the first thing that comes to mind is- International Organization for Standardization however in photography, it stands for something else. ISO is a camera’s sensitivity to light. It is usually displayed in numbers like 100, 200, 400, etc. When the light in the surroundings is more, the ISO is set to a lesser number and vice-versa. 
During the olden days, people used film rolls to click pictures. ISO was the rating given to a film so that one could understand how sensitive it was to light. Back then, it was important to know this beforehand so that photographers could click pictures at any time and the condition of their surroundings wouldn’t affect the quality of the pictures. 
Today, with more advanced instruments, predicting or modifying exposures is simpler. In digital cameras, the option of setting/ controlling ISO is given. 

What is the functionality of ISO?
The ISO setting on the camera is like a volume dial. If you want darker images, you turn it down to 100 or 200 and for brighter images, you turn it up to 3200 or 6400 or anywhere in between if you want something very specific. 
Now, you are probably wondering that with this functionality, you don’t need to care about the surrounding light. Well, unfortunately, that’s not how it works. When you increase the ISO, you also increase the gaining. A grainier image will be less dynamic and less sharp.

 
So, what exactly are grains? These are tiny little dots that take shape on your image like static on a television. Grain and noise are sometimes used synonymously but they have different meanings. Film grain is more like texture that brings to the life the images. Noise is a defect of the sensitivity of the camera to light. When your camera can’t interpret the light or isn’t sensitive enough, the result is noise. 

Let us understand some differences between grains and noise. 

GRAINS	NOISE
The size of grains depends on the film sensitivity. More the light, bigger the size.	Noise is always the size of a pixel, regardless of the ISO setting.
Film grain is color neutral.	Digital noise has both luminance and color differences.
Grain doesn’t have any banding or patterns.	Noise may have banding and patterns.
Grain usually refers to Film cameras	Noise usually refers to Digital cameras

Effects of low ISO on photos
Base ISO is the lowest a camera can go. Many cameras have that setting at 100. At this value, the camera has a super dynamic range of colors, sharpness with the least amount of noise. Once you start going higher, you start getting noise in your image. 

Outdoor photography on a bright sunny day or landscape photography is where you can use the lowest of ISO settings because there’s plenty of light. A low ISO setting is also preferable for portrait photography. 

Effects of high ISO on photos
Higher ISO is the best when the light is low or when the exposure is short. So, it’s usually used in astrophotography or while shooting the milky way because in these cases, the grains add a layer of sharpness. Low ISO in these cases will produce blended images. 

How should one use their ISO?

• Adjust the shutter speed
• Decide the aperture 
• And then set your ISO.