This article is written in the context of Digital SLR (single lens reflex), which are combing the market like hot cakes nowadays.
ISO, which stands for International Standards Organization, refers to the how sensitive to light the camera sensor is for a Digital SLR.
Quite a handful of new photographers do not really understand the relationship between ISO, aperture and shutter speed settings, which determines the exposure of the photograph.
It is important to understand what ISO is as it affects the outcome of your image as well as its quality.
We are lucky that SLR has gone digital and thus changing the ISO setting can be done by simply pressing a few buttons.
Could you imagine the good old days where films are used? You need to replace the roll of films and you may need to carry a few rolls with you when traveling.
The typical range of ISO are 50, 100, 400 and up to 1600 or above for newer Digital SLR models.
Simply, a low ISO setting is desired to achieve good image quality while a high ISO setting would most likely produce grainy image with loss of details due to noise produced by the camera due to distortion caused by "over-amplification".
It is not necessary bad to have a grainy photograph especially for portraits, as it creates a moody effect, which could make the photograph more attracting to viewers.
There is a strong relationship between ISO, aperture and shutter speed where all photographers should know and understand.
Knowing this relationship will allow you to take more creative images and images that you always desired.
Instead of explaining the technical terms, I will use examples to illustrate the relationship to make learning more interesting.
Say for example you want to take a landscape under a bright sunny day, you will most likely use a relatively small aperture of say f/9.
In this case, if a high ISO is set, there would be a risk that your photograph be overexposed.
Thus in this case, a low ISO is desired and once again, a low ISO can yield better quality image and color.
If you are in a well-lit room and you don't have a tripod and not going to use flash, you may overcome this situation by selecting a high ISO of say 800, together with a wide aperture.
In this case, blurring due to camera shake can most likely be avoided.
If the same aperture size and shutter speed is used in the same environment and ISO is set to 100, very highly the photograph will be blurred.
You can do this simple experiment in your own room and will soon understand what I mean.
For night photography (without using of flash), a tripod is a must.
With the use of stable tripod, camera shake can be avoided and thus, a low ISO is always desired.
The choice of ISO is significant for night photography as you can better observe the quality of the image and its color with different ISO settings.
Try doing this experiment yourself and you can easily see for yourself how the image quality differs with the use of different ISO setting.
Normally for night photography, a slow shutter speed is desired and thus a low ISO is selected.
This can go on and on with so many examples to share.
But in general, the ISO setting plays a vital part in determining the aperture and shutter speed of your camera.
For a given situation, using a low ISO will mean that you have to set longer shutter speed, or use a wider aperture, or a combination of both.
Using a high ISO will mean that you have to set a faster shutter speed, or use a smaller aperture, or a combination of both.
Hopefully by now, you will understand the importance of ISO setting and how it effects aperture and shutter speed setting of your camera.
Do keep practicing until it becomes a second nature to you and with this knowledge, it can help you produce creative images you always desire!