Page 41 - Learning How to Photograph with your DSLR Camera 2nd Edition Jan 2021

Lesson 7: ISO, When & How to Adjust It

What is ISO?

Think of ISO as the sensitivity of your sensor to light. The lower the ISO number the less
sensitive and the higher the ISO number the more sensitive.
If you recall in the days of film, we had different film speeds. For example, ASA 200, 400,
1000. In those photos with higher ISO like 1000, grain could be seen in your photograph.
These were tiny dots in the film that gave it a grainy appearance (noise).

In the digital era, we still have noise in our images at higher ISOs. Instead of dots, they
are darker pixels that appear as grain like in the days of film.
As a rule, when it is bright outside an ISO of 100-200 would suffice. A cloudy day you
might bump it to 400. Indoors, without a flash 800 might work or even higher. As you
can see your ISO is dependent on light and it is most useful for low light situations.

Figure 16 ISO range

From the scale above you can see that the numbers double when increased. These are
stops. For example, in a dimly lit room: Each stop increase makes the image brighter
while decreasing the ISO will make the image darker.

Figure 17 ISO Stop Scale

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