ISO (Exposure Series Part 5 of 5)

Myfotoguy series on exposure part 5 of 5
 
ISO Review
The higher the number the more sensitive the image sensor is and the less light it needs to create an image. The lower the number the less sensitive it is and more light will be required. ISO setting follow a standard sequence, a typical range:

100; 200; 400; 800; 1600; 3200
Each one is twice as sensitive as the next. If you change your ISO setting from 200 to 400 you will gain one stop more exposure.
 

Effects of ISO
Normally, you might increase or decrease your ISO when the other parts of the exposure triangle don’t allow you to achieve proper exposure for the desired effect you are after.

Most photographers shoot with the lowest ISO possible (many DSLR cameras start at ISO 100 or 200). This is because the higher the ISO becomes, the more grain and digital noise get added to your image (see example below).

The image series below illustrates the difference in ISO settings. Click here or on the image to see the difference in settings. Depending on your browser, once the image is loaded you may need to click the image to see it full size. The ISO 3200 version on the right is much grainier (especially on the right side of the image).


When I increase my ISO it’s usually because I need a faster shutter speed or more depth of field and there’s not enough light to capture the scene without increasing the ISO.
 

Situations where you might need to increase your ISO to capture the scene.

  • Churches – Often the lighting is poor.
  • Gymnasiums – Lighting is usually better than a church, but higher shutter speeds are typically needed to stop the action, which requires higher ISO.
  • Museums – Often the lighting is poor, flash is prohibited, and flash can make it challenging to capture images behind glass.
  • Around your home – There are many times you might want to capture an event at home without flash and higher ISO is the only way
  • to capture the image.

Note: These are situations where flash is an undesired option because you don’t want to disturb the mood, or the subject is too far away for the flash to be effective, or for creative decisions.

 
What about the grain/noise?
 Through experience you will learn to make decisions regarding ISO settings. Some questions to ask yourself:
  • Will noise ruin the image?
  • Is some noise better than no image at all?
  • Is the noise acceptable?

Increasingly as technology advances cameras are getting better and better at handling noise, even at higher ISO settings. Proper exposure also plays an important role in keeping unwanted image noise at bay. An underexposed image will usually have more grain and digital noise than a properly exposed image. Other factors such as extreme heat can effect the noise. In post-processing, recovering shadow areas by extreme changes to bring out detail will sometimes bring out noise too.

There is software available that will help reduce the noise. I use Noise Ninja for most of my work, or the built in Noise reduction in ACDSee Pro. I didn't post it here, but as a test I ran Noise Ninja on the ISO 3200 image above, the results was an image that looked more like the ISO 800 version. Noise reduction software works! Some other programs that reduce noise:
Nik Dfine
Neat Image


So, what do you do to reduce noise?
If your camera has it, do you use Auto ISO?
How do you decide your ISO setting?

 

 
Articles in this series:
Part 1 - The Exposure Triangle
Part 2 - Stops, Values, and Sensitivity
Part 3 - Aperture
Part 4 - Shutter Speed
Part 5 - ISO

 
 
 

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