A Photo Story

The correct exposure of a photo is made up of three parts.  Aperture controls the depth of field, shutter speed controls the speed of the shutter (obviously!), and ISO controls the sensitivity of your film or camera sensor.  All three parts contribute to various creative aspects of a photo.  All three parts must be set correctly in conjunction with each other to achieve a photo that records the correct amount of light for a correctly exposed photo.

This is part 3 of my tutorials on exposure: ISO settings.  Go back and check out parts 1 and 2 detailing how to creatively use aperture and shutter speed in your photos.

What is ISO?

Bryan Peterson (a professional photographer and best-selling author) describes the effect of ISO on exposure by thinking of the ISO as a worker bee.  So for instance, if you were taking a photo using an ISO of 100, it would be like using 100 worker bees.  If you were taking a photo using an ISO of 200, it would be like using 200 worker bees.  These worker bees use the light coming through the lens to make an image.  So, 200 worker bees would record the image twice as fast as 100 worker bees.

In the film world, ISO was a measure of the speed of the film.  So, if you use ISO 400 (400 worker bees) your film would make an image faster than a film of ISO 100.  In the digital world, ISO still relates to the speed or sensitivity of the camera sensor with regards to light.  You can set your digital camera to different ISO speed and record images faster or slower depending on the situation of light.  The best part is that you don’t have to change the roll of film to change the ISO.

How does ISO affect the exposure?

ISO relates directly to the shutter speed.  Higher ISO numbers mean higher shutter speeds can be used at the same aperture (f/stop).  So, if I am taking a sunny outdoor photo at f/8 and ISO 100, my camera tells me that my shutter speed needs to be 1/200 seconds for a correct exposure.  Now, I’ll double the ISO to 200 and see what happens.  This same sunny outdoor photo at f/8 and ISO 200 now needs a shutter speed twice as fast at 1/4oo seconds.

Bottom line is the higher the ISO, the faster the shutter speed can be.

When do I use a higher ISO?

There are many times when using a higher ISO can be favorable in a photo.  Lets say that you are at a concert, museum, or church that does not allow flash photography.  When you turn off the flash, your camera may be using a shutter speed that is too slow (1/60 and slower) to hold the camera steady resulting in blurry photos.  Set your camera to a higher ISO and  you can take a crisp photo without a flash because the higher ISO allows the use of a higher shutter speed.  If your camera is on ISO-Auto, the camera should choose the highest ISO setting available.

Higher ISO numbers are used in low light situations to achieve a correctly exposed image at a desired shutter speed.  I use high ISO at nightly sporting events where I want my shutter speed to be higher than 1/125 so that I can still stop the action of the players.

Low ISO numbers are used in sunny or bright situations where a slower shutter speed can record more vivid colors in the photograph.  In sunny settings, shutter speed does not become the difference between a blurry photo and a crisp photo.  In low light settings, shutter speed can become that difference.

What are the drawbacks of using a higher ISO?

Typically you will want to use the lowest ISO setting possible for your photos.  In digital photography, high ISO settings mean more noise in the photo.  Noise comes across in an image as distracting colored dots all over your photo.  In film photography, high ISO film means the image appears more grainy than on low ISO film.  Take a look:

1/2 sec, f/6.3, ISO 200                                                                        1/4 sec, f/6.3, ISO 400

1/10 sec, f/6.3, ISO 800                                                             1/20 sec, f/6.3, ISO 1600

1/50 sec, f/6.3, ISO 3200                                                         1/100 sec, f/6.3, ISO 6400

You can see from the photos how the ISO affects the shutter speed.  Also, you can see that by ISO 6400 the noise really distracts from the photograph.  These images are taken on a Nikon D300 (DSLR) which is known for dealing well with noise at high ISO settings.  Many point and shoot type cameras become noisier much quicker.  Cameras with smaller sensors exhibit more noise at higher ISO settings.  Learn how your camera works and what kind of photos you get from it.

At a high ISO setting, you can achieve much higher shutter speeds, but at the price of distracting noise in your photo.

Remember to put the ISO back where you found it!

ISO is an exposure setting that usually is forgotten when taking photos.  Remember to try a higher ISO in low light photography, but, also remember to put it back to the low 100 or 200 setting when you are done.  There is nothing worse than taking a gorgeous landscape photo and later realizing that your ISO was still set at 800 from the night before therefore ruining your wonderful photo.