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Monday, 25 October 2010

What Is ISO?

Author: Lyn Murphy and Peter L Murphy

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"ISO stands for International Standards Organization, and it is a standardized industry scale for measuring sensitivity to light. This can be used in relation to how sensitive camera film is to light, but more commonly today, it pertains to the sensitivity of a digital image sensor. ISO is measured in numbers, with the lowest number being the least sensitive to light, (e.g. ISO 50 or 100), and the highest number being the most sensitive to light, (e.g. ISO 6400)." From an Article by Jonathan Wylie entitled What Does ISO Stand For?
100 ISO is generally accepted as 'the norm' in standard outdoor photographic conditions. This will give you lovely crisp shots with little noise or grain.
Most people tend to keep their digital cameras in 'Auto Mode'. This means the camera selects the appropriate ISO setting depending upon the shooting conditions (it will try to keep the ISO levels as low as possible), but most cameras also give you the opportunity to select your own ISO setting.
When you do override your cameras Auto Mode, and choose a certain ISO setting, you'll notice that it combines the aperture and shutter speed needed for a well exposed shot. For example, if you bumped your ISO up from 100 to 400 you'll notice that you can shoot at higher shutter speeds and/or smaller apertures.
When choosing the ISO setting I generally ask myself the following four questions:
  1. Light- Is the subject well lit?
  2. Grain- Do I want a grainy shot or one without noise?
  3. Tripod- Am I using a tripod?
  4. MovingSubject- Is my subject moving or stationary?
If there is plenty of light, and I am using a tripod, or my subject is stationary, I can use a pretty low ISO rating e.g. 100 ISO, and my resulting shot will be crisp and clear.
However if it's dark, I don't have a tripod and/or my subject is moving, I might consider using ISO 400-800, as this will enable me to shoot with a faster shutter speed and still expose the shot well.
Of course the trade off in this increase in ISO will be noisier (grainier) shots.
Situations where you might need to increase the ISO to higher settings include:
  • Indoor Sports Events- where your subject is moving fast yet you may have limited light available.
  • Concerts - also low in light and often 'no-flash' zones
  • Art Galleries, Churchesetc- many galleries have rules against using a flash and of course being indoors are not well lit.
  • Birthday Parties- blowing out the candles in a dark room can give you a nice moody shot which would be ruined by a bright flash. Increasing the ISO can help capture the scene.
If you want to gain more control over your digital camera then it is important to have an understanding of ISO settings. This very important aspect of digital photography will allow you to experiment with different settings and discover how they impact the resulting images.
Always remember to refer to your camera manual for further advice.
My husband and I have just set up our own online digital camera shop. Photography is a passion for Pete and we will be collaborating to produce a series of articles on the subject.

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