Camera ISO – an introduction

Camera ISO is one of the three pillars of Photography (the other two being Shutter Speed and Aperture) and to get the most out of their photography, every photographer should thoroughly understand it.


So what is ISO?  ISO is the level of sensitivity of your camera to available light.  The lower the ISO number, the less sensitive it is to the light while the higher the number the higher the sensitivity to available light.


The component within your camera that can change the sensitivity is called the “image sensor” or simply the “sensor”.  It’s the most important part of a camera and it is also responsible for gathering light and transforming it into an image.  With the sensor’s increased sensitivity, the camera is able to capture images in low light situations without having to use a flash.  Keep in mind though that higher sensitivities come at a price, when ISO sensitivity increases so does the amount of grain or “noise” within the image captured.


Every camera has a “Base ISO” which is the lowest ISO number that a sensor can produce to get the highest image quality without adding noise.  With this in mind, you should find out what the Base ISO is for your camera and try to stick to that ISO (whenever possible) to get the highest image quality.


Typically, ISO numbers start from 100-200 (Base ISO) and increment in value in geometric progression (power of two). So, the ISO sequence is: 100, 200, 400, 800, 1600, 3200, 6400 and etc. The important thing to understand, is that each step between the numbers effectively doubles the sensitivity of the sensor. So, ISO 200 is twice more sensitive than ISO 100, while ISO 400 is twice more sensitive than ISO 200. This makes ISO 400 four times more sensitive to light than ISO 100, and ISO 1600 sixteen times more sensitive to light than ISO 100, so on and so forth. What does it mean when a sensor is sixteen times more sensitive to light? It means that it needs sixteen times less time to capture an image!


ISO Speed Example:

ISO 100 – 1 second

ISO 200 – 1/2 of a second

ISO 400 – 1/4 of a second

ISO 800 – 1/8 of a second

ISO 1600 – 1/16 of a second

ISO 3200 – 1/32 of a second


In the above ISO Speed Example, if your camera sensor needed exactly 1 second to capture a scene at ISO 100, simply by switching to ISO 800, you can capture the same scene at 1/8th of a second or at 125 milliseconds! That can mean a world of difference in photography, since it can help to freeze motion.


Use the Base ISO as a starting point, then if there is more light than required at Base ISO then feel free to lower the ISO, and if there is less light, then increase the ISO.  Keep in mind, the higher the ISO, the more noise to the image.


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