Exposure
To understand how the 3 values (ISO, diaphragm and shutter speed) function together when exposing a photograph, we will use another example.
Let's imagine we are shooting a photograph with ISO 400 and light measurement results in f/5.6 at 1/30.
What happens if we change the film or the function in digital cameras to an ISO 100? How do we compensate the shutter speed or diaphragm?
The first things we need to consider is that ISO 100 is less sensitive than ISO 400. How much less sensitive is it? 2 points. Therefore, if ISO 100 is 2 points less sensitive than ISO 400, it means it will need 2 points more of light for the photograph to be properly exposed. In the first chart, we gave it 2 points more light varying the diaphragm; and in the second chart, we gave it 2 points more light varying shutter speed.
