Digital Photography: the ISO setting

“The truth is that our finest moments are most likely to occur when we are feeling deeply uncomfortable, unhappy, or unfulfilled. For it is only in such moments, propelled by our discomfort, that we are likely to step out of our ruts and start searching for different ways or truer answers.”  -M. Scott Peck

 

The level of difficulty for this discussion of ISO settings: beginners

Understanding ISO is surprisingly easy.

  • Sensor sensitivity to light: ISO is a carryover from the days of film photography. It referred to the amount of sensitivity to light of a particular type of film. Similarly in digital photography, ISO indicates the degree of sensitivity to light of the camera’s light sensor. This sensitivity is adjustable. The higher the ISO, the more sensitive is the sensor to light. This greater sensitivity of the sensor allows the use of a faster the shutter speed and/or smaller aperture diameter than would be needed if the ISO (and sensitivity to light) were lower. A faster shutter speed is usually an advantage because it increases the probability that the image will be sharp.
  • Electronic noise: The disadvantage of high ISO however, is that more sensitive pixels are more likely to be activated by electron movement within the sensor itself, rather than by the light. This accidental firing of pixels produces red and green pixel-sized dots (color noise) and mottling in areas of uniform lighting such as blue sky (luminance noise). In addition to ISO, the amount of noise within an image depends upon the sensor type and quality.Color noise (also called chrominance noise and chromatic aberration) shows up most readily in the darker areas of your photo when viewed at a magnification of 150% or higher (200% makes this easier for me). Luminance noise (also called contrast noise) areas of uniform color and lighting, such as blue sky, when viewed at a magnification of 150% or higher (again, 200% is easiest for me).
  • Which ISO is best? To minimize the amount of electronic noise in your images, use the lowest ISO setting that allows you a shutter speed fast enough to achieve the effect that you want for that image. Usually, the preferable effect is sharpness. For instance, to “freeze” the motion of a person walking, a shutter speed of at least 1/125 sec is needed. To stop the motion of a person running, a minimum shutter speed of 1/250 sec is needed. In order to have sharp images of sporting activities often requires a shutter speed of at least 1/500 sec. If the light on the scene is low, shutter speeds this fast will not be possible with a low ISO setting, even when using a large diameter aperture.  When in this situation, increase the ISO only as much as is needed to achieve your desired shutter speed.   This increased noise level just needs to be tolerated or, better yet, removed with editing software. A high ISO is also necessary in very low light situations such as night photography, especially night sky photography of the stars.
  • When slow shutter speed is needed, a low ISO is helpful: Sometimes a blur is the photographer’s desired effect. The most common example is flowing water or waves that one wants to appear smooth or hazy. In this case a long shutter speed is needed, typically 2 to 15 seconds. Using the lowest ISO setting (and a small diameter aperture like f/16 or f/22) will help to get shutter speeds that last this long without overexposing your image. Another example of a specific need for a low ISO setting is when the desired effect is a blurring of a person walking or of moving automobiles, in order to convey the feeling of speed.
  • For those people who do not want to mess with ISO settings, use your camera’s program option for landscape, portrait, close up, action/sports and night photography. Your camera will then automatically provide you with the ISO setting which is usually the best.

Condensed version for those in a hurry:

  • The higher the ISO number, the more sensitive the camera’s sensor is to light.
  • The higher the sensor’s sensitivity to light, the more electronic “noise” the image contains.
  • To minimize the amount of noise, use the lowest ISO number that allows a fast enough shutter speed to achieve the effect that you want (usually sharpness).
  • Cameras with program options such as landscape, portrait, close up, action/sports and night photography, will automatically provide you with the ISO setting which is usually the best for that purpose.
  • Electronic noise can be removed with editing software. However bold noise removal creates loss of sharpness or decreased saturation of color.

When noise in an image usually does not matter: When your photo is going to be displayed on the web or you will make prints no larger than 4 inches by 6 inches, noise will usually not be apparent unless the noise level is very high. (But you never know when you will shoot a remarkable image that you wish to enlarge and print. A high noise level will require special processing for removal).

Noise removal

  • Every digital image contains noise regardless of the ISO or quality of the camera.
  • Noise removal is the first step of image processing by professionals.
  • High ISO creates much more noise than usual, making its reduction even more important. Noise removal is accomplished with editing software (luminance noise reduction and color noise reduction) such as the software that came with your camera, Photoshop, Photoshop Elements, Lightroom and many other editing programs. (The best, and easiest to use noise reduction software that I know of is Nik software’s Dfine program). However large amounts of noise reduction produce slightly blurred images from luminance noise reduction and/or unsaturated (faded) color from color noise reduction. A slightly blurry image can sometimes be saved by applying extra sharpening with your editing software. Desaturated color can be easily fixed by adding a little saturation with editing software.

I welcome comments, criticisms and questions about specific photography issues that you may be experiencing.

I am available at NaturePhotoRehab.com where I help people have their images transformed into impressive works of art that they are proud to either hang on their own wall or give as a gift.

J. Michael Harroun©2012 NaturePhotoRehab.com

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6 comments on “Digital Photography: the ISO setting

  1. […] Digital Photography: the ISO setting (naturephotorehab.wordpress.com) […]

  2. Mary Mageau says:

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  3. musicgal2012 says:

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