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14.7 - Stop & ISO Example

By understanding that an ISO 800 setting is three stops more sensitive than ISO 100, you now know that you can use a shutter speed that's three stops faster.

Let's say, with an of ISO 100, you're photographing a horse at twilight.

The horse is called Second Chance.

There's enough light to use an exposure of f/4 with a shutter speed of 1/15th of a second.

ISO 100

f/4

1/15th

1/15th of a second is a slow shutter speed.

Second Chance, the horse, will be blurry if she's moving.

And, you'll get blur from camera shake.

So, you switch to ISO 800.

The sensor is now more sensitive to light.

So, you can use a faster shutter speed—three stops faster.

ISO 100	f/4	1/15th
ISO 800	f/4	1/125th

Here's how to count the number of stops in this example.

ISO 100 to ISO 200	ISO Doubles	1 Stop More Sensitive	1/30th
ISO 200 to ISO 400	ISO Doubles	1 Stop More Sensitive	1/60th
ISO 400 to ISO 800	ISO Doubles	1 Stop More Sensitive	1/125th

Second Chance will be sharp.

That's because you're able to use 1/125th instead of 1/15th.

You were able to change the shutter speed by three stops because you changed the ISO by three stops.

Now, let's look at how Stop is spoken in the country called lens opening.