Exposure

If photography means “writing with the light”, we can think that light is our ink. But what is being played the role of the pen? and the sheet?
Figuratively speaking, I would say that the pen is the lens through which the light (ink) flows, and the sensor is the sheet on which the light is laid, leaving a trace.
In this metaphor, the exposure is nothing more than the amount of ink being spilled on the paper. Too much ink “burns” the paper and will not allow us to read anything, too little produces an opposite effect, but no better.
If we think about it, there are 3 parameters that we can control to determine the correct amount of ink:

1. our speed scrolling the pen to paper: the faster the flow less ink will be deposited on the sheet;
2. the pen we use, and in particular the width of his sphere or his nib: wider means more ink deposited in the same fraction of time;
3. the surface on which we write: there are sheets which absorb more and less ink.

For photography, there are exactly the same parameters and they are called:

1. shutter speed
2. aperture
3. ISO

From next post, I will start talking about the shutter speed.