Photography basics – What is ISO?

In digital terms, ISO refers to the sensitivity of your camera’s image sensor to the amount of light present. Generally, the higher the ISO value, the faster your shutter speed will be, and consequently the increased ability to work in lower amounts of light.

A typical range for ISO values in entry-level cameras is ISO 100-1600 with a boost to ISO 3200. This can be broken down into different levels: 100, 200, 400, 800, 1600, 3200. Each of these levels are called “stops” ISO 100 to ISO 200 refers to a single stop or “one stop”.

Say your ISO value is now 100. You are now planning to take a photo and your shutter speed reads 1/40 secs. Generally speaking, the minimum shutter speed you need in order to get a relatively sharp image is 1/F where F refers to the focal length of your lens (Read more about minimum shutter speed). For this scenario, you do not have to do anything except pressing the shutter if the focal length of your lens is 30mm (or less). If your focal length is more than 40mm but your lens has Vibration Reduction (VR) technology, you might be able to make the shot. This is also provided that your subject is stationary (Read this to find out why).

Apart from these two exceptions, the other alternative solution would be to increase your ISO value by one stop or more. As mentioned above, an increase in the ISO value means a boost in shutter speed. A “one stop” increase relates to a “doubling” in the shutter speed. In this case, by switching to ISO 200, your shutter speed will read 1/80 secs which is more than likely enough to do the job.

However, it does not always mean that since the higher the ISO the better, it is ideal to use it at the highest value of ISO 3200. It should be noted that with the increased convenience of a faster shutter speed through boosting the ISO, image quality is compromised. Therefore, the user has to decide what to priortise: go all out to get the shot but at the expense of sacrificing image quality, or foregoing the opportunity entirely. Sometimes, getting the job done is better than going home empty-handed.

Other choices are also available. Use an external flash, or, a more expensive alternative is to  switch to a lens with a larger aperture (meaning lower aperture value such as 1.4 or 2.8) as larger apertures allow more light to reach the camera’s image sensor, thus achieving a faster shutter speed. A “faster” lens would be preferred on occasions when there are limitations to using a flash.

Related posts:

1. Photography basics – What is the minimum shutter speed you can use?
2. Photography basics – Mode dial (Manual)
3. Photography basics – Vibration Reduction (VR)
4. Photography basics – Choosing your first lens (Part 2)
5. Photography basics – Mode dial (Program)