ISO Sensitivity Value

There are basically three camera settings that determines how bright or dark your photo will be:

1. Shutter Speed
2. Aperture
3. ISO Sensitivity Value

Let me first expound on #3, the ISO Sensitivity or ISO Speed or simply referred to as "ISO" in the photography world.  I will neither elaborate why it was called ISO nor explain its technical details, but will rather stress on its function.




The ISO setting on the digital camera adjusts the image sensor's sensitivity to light.  It determines the amount of light that exposes the image sensor.   All digital cameras record images in an electronic form. The image sensor, which is the heart of a digital camera, records an image when you take a picture, which is then immediately saved in the camera's memory card.  This is the equivalent counterpart to film in an analog camera.  

The most common ISO value in digital cameras are 100, 200, 400, 800, 1600.  Some cameras can go down to 50 and  more advanced camera can go up to as high as 25600.  


So what do these values mean?

In general terms, the higher the ISO value, the brighter your photo will become because the camera will bring in more light to the image sensor.  But always keep in mind the other two factors that can affect the brightness of your photo -- shutter speed and aperture.   

A high ISO is useful when shooting in low light (dark) conditions.  Select a low ISO setting when shooting in bright light.   Using a high ISO sensitivity setting though has its own trade-off which you may like or dislike depending on what you want to achieve.  With a high ISO, images taken are more susceptible to "digital noise" (the equivalent to "grain" in film camera).  If your purpose is to obtain high image quality, it is recommended to use a low ISO as much as possible .  However, shooting in dark situations with a low ISO may result to blurry images because of the "camera shake effect".  In my succeeding post, I will further talk about "digital noise" and "camera shake effect", and how to deal with these issues.  

Below are sample photos taken at low and high ISO respectively. The second photo shows how high ISO setting produces digital noise which affected the overall image quality.   The noise is noticeable on the darker areas of the photo, see those tiny whitish little dots on the upper right corner of the second photo?   Digital noise is more evident on large printed photo or when you zoom-in on the image.  

ISO 100

ISO 12800

In most digital cameras today, ISO setting of up to 400 will produce good results.  But again, it is always best to use the lowest ISO setting possible (normally 100 or 200).  You may also let the camera select the ISO automatically by using the "Auto ISO" feature (I'm not certain whether all cameras support this feature).  Just specify the range of ISO values where your camera can automatically choose from.  If you use this feature, make sure that the upper limit ISO value will not produce much digital noise, and I suggest using 100 to 400 or in certain cases 100 to 800.       

As an exercise and also to familiarize yourself with your camera, shoot a few shots using different ISO settings and compare the results and find out which setting or settings will suit your taste.

Keep on shooting!