What is ISO? How Does It Work?

I don’t care much for a bucket full of technical terminology. Let’s use language we can all understand. Information for the masses, yeah!

The ISO setting is common to all digital cameras and I’ll show you how, why and when to change it. You’ll be on your way to becoming one of the more enlightened photographers of the day.

Testing ISO by Marc ManthaChallenging the ISO myth.

I’ve updated the test challenge with some shots I took today.

NOTE: Some have tried this test hand held, then cling to the myth because the exposure changes…and of course it will. That’s because it’s not possible to take the exact same shot in succession holding a camera. The slightest movement from one shot to the next changes the outcome.

Setting up for the ISO demonstration shots:

  • Tripod.
  • Panning head locked in position.
  • Remote shutter release.
  • Repeat the same shot at ISO intervals 100, 200, 400, 600, etc.
  • Upload to the blog.
  • See with our own eyes.

Results: (see the film strip on the right)

The exposure for each is about the same. Pretty boring huh?

If the camera sensor is more sensitive to light as the ISO setting goes up, why doesn’t the shot get lighter?

That’s the right question.

There’s a balancing act going on inside your camera.

Each time the ISO gets higher with more light sensitivity to the camera sensor, the shutter speed gets faster and faster letting in less light to the sensor.

Higher ISO + faster shutter speed = no significant change in exposure outcome.

Together, they create a balance.

Sort of canceling each other out with the benefit of a faster shutter speed.


Increasing the ISO value boosts your shutter speed without significant change to the exposure.

It’s that simple.

How, when and why to use ISO.

Use the ISO function in any low light situation where you need to boost the shutter speed, better avoiding camera shake (blurry photos).

  • You can’t change the ISO setting in Full Auto Mode. The camera makes all the decisions. You Need to use P (Program Shooting mode or any other semi automatic or manual shooting mode you are comfortable with).
  • Light indoors is most commonly inadequate. Even in a room your eyes perceive to be well lit. The camera shutter needs to remain open longer. This causes blurry photos when you hold the camera. Good time for a higher ISO.
  • Many cameras will display the shutter speed when you partially depress the shutter button. Do this while pointing at your proposed subject(s). You’ll require about 1/300 of a second on telephoto (zoomed in) shots and about 1/30 of a second on wide angle shots (zoomed out). Results will vary depending on the camera and lens, so this is a guideline. Need more speed? Increase the ISO.
  • Use higher ISO settings outdoors on very overcast (heavily clouded) days or in the shade where natural sunlight in compromised.
  • ISO becomes more important to Digital SLR shooters who, when implementing other functions, features and lens capabilities still need an extra boost to the shutter speed. ISO may be the last consideration.
  • Increasing the ISO is not a concern in most cases when shooting still life using a tripod and a remote shutter release (or self timer) as there is very little or no risk of movement. Slow shutter speed + movement = motion blur.

What about noise?

There is some notable digital noise (graininess)  that can creep into photos shot at the highest ISO settings. My take on it? I’d rather have some digital noise than a memory card full of blurry shots. ISO performance in digital cameras keeps getting better over time.

Go out and find something you weren’t looking. Have fun!

MAMA Photography

MAMA supports the creative minds of the planet earth. If you come across somebody doing anything interesting and out of the ordinary, or just something that makes you smile, we’d like to know about it.

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