Understanding ISO

ISO chart

ISO refers to the light sensitivity of the film or a sensor in a digital camera. It ranges from 25 to 6400 (or even more for some cameras). However for most camera it will start at 100. 

Sensitivity increases with increasing ISO numbers. Prior to digital camera we used to buy film with different ISO ratings. Most commonly available for consumers of point and shoot camera was rated at ISO 400. I remember my parents camera Yashica MF2 had only 2 settings for ISO - 100 & 400. What that meant was for correct exposure we will need to use either ISO 100 or ISO 400 film with the correct setting. 

ISO 100 would be used for places which are adequately lit. Like direct sunlight or a properly lit room. In case of darker lighting conditions the ISO would be increased to get perfectly exposed images. 

It's easy to underexpose or overexpose the image with wrong ISO. This is normally in coordination with the shutter speed and aperture. 

In the images below only ISO was changed. Shutter speed, aperture and all other settings remained the same. 

ISO 100 . Under Exposed

ISO 400 . Intended Exposure

ISO 1250. Over Exposed

Thankfully with the advent of digital camera we can change the setting with a button and the image sensor would respond to it.

ISO settings are inversely proportional to the amount of light available. However try and use the lowest possible ISO setting for any image to ensure good quality. Image quality decreases with increase in ISO. 

Do try taking pictures in different lighting conditions with varying ISO settings to see the difference. 

Kunal