Learning about ISO settings -

  I am beginning to understand exactly how the ISO setting is related to aperture and shutter speed. The sensor is the part of the camera that records the available light. The aperture determines how much light will hit the sensor, and the shutter speed determines for how long the light will hit the sensor. SO - the ISO setting determines how sensitive the sensor is to the light. In other words, the ISO setting determines how bright your image is going to be.
   Deciding which ISO setting to use depends on multiple factors: the effect you want to achieve, the amount of light available, whether you want to use a particular aperture setting, and how much noise you're willing to accept in the digital image.

f5.6   1/42   ISO 64

  

   For this first set of images,  I decided to leave the aperture set at 5.6, so that I could see the relationship between a variable shutter speed and ISO.  Here is a shot taken at the lowest ISO my camera allows me to use. The shutter speed is not slow enough for camera shake to be a problem, */and at this ISO the sensor is not as sensitive to light as it would be at a higher setting. Note the deep shadows.

f5.6   1/75   ISO 100

                                                                                                                                                   

Here is a picture shot at a more commonly chosen ISO, 100.  On a sunny day, which this wasn't, this setting would give you a clean crisp shot with no noise, and a slightly faster shutter speed. I noticed that as the ISO setting rose, the shutter speed shortened.  The color in the first photo is a little more saturated than in this one, but this is still acceptable.

f5.6  1/140  ISO 200

It's a little boring to keep taking the same shot but I thought it would be good for comparison purposes.  Here, the ISO setting is doubles, which caused the shutter speed to roughly double too, to compensate for the increased sensitivity of the sensor.

f5.6  1/250  ISO 400

You can see the mathematical relationship developing here. Every time the ISO doubles, the shutter speed comes close to doing the same. This is because the sensor is becoming more sensitive to light, so the shutter must shorten the time that light is allowed to hit it.

f5.6  1/480  ISO 800

With the ISO set at 800, this photo is beginning to look washed out. The colors are less intense and the detail is less fine.

f5.6  1/1000  ISO 1600

Again, the ISO has doubled, and the shutter speed is more than twice as fast. The color is duller yet, almost a gray green, and the yellow flower in the center is much paler.

f5.6  1/2000  ISO 6400

I've jumped to the last photo - the highest ISO I could get. At this setting the sensor is extremely sensitive to light, so the colors are not accurately captured. The shutter speed and aperture would both have to be changed to get proper exposure, and even then it might not be possible with an ISO setting this high. If you enlarge this picture you will see enormous noise, or what would be called grain if this were taken with a film camera.

These last two photos show the effects you can get by playing with the ISO setting. The picture on the left had an ISO setting of 100. The one on the right is ISO 800.  To me, the one on the left looks fresh and bright, while the one on the right looks old and faded.