So what are the three pillars of photography? These are the three control points we will call them, that we use to control the exposure - exposure is the amount of light paying through the lens and hitting our film or sensor. And they are, ISO, Aperture(F-stop), and finally shutter speed.
Let's start with ISO. what is ISO? Well, ISO stands for International Standards Organisation and it refers to the industry norm for sensitivity of emulsion based film, with 100 ISO being not so sensitive (and the standard ISO used by most people) to 1600 ISO which is extremely sensitive to light. That's basically it. We can see in the image below, that the lower the ISO the clearer the image and the higher ISO the grainier it gets. Now if you also notice, that directly correlates to the Aperture or F-stop.
Now let's take just a half step back here. "What the heck is F-stop?". "The f-number of an optical system such as a camera lens is the ratio of the system's focal length to the diameter of the entrance pupil. It is a dimensionless number that is a quantitative measure of lens speed. It is also known as the focal ratio, f-ratio, or. f-stop." Thank you wikipedia! I know that's a bit of a wordy explanation but it essentially says, F-stop is how big the hole in your lens is. The smaller the number, the bigger the hole. And vice versa. So what does the hole size mean for us? A bigger hole let's more light in, which is good in darker areas. But it also does something really interesting with our depth of field. If we focus on someone that's close to us, and take the shot you will see that the background behind the subject is blurry or soft. This is called bokeh. Now before we get too carried away, what we need to remember is that our aperture will either let more light in, our less.
If we look at the triangle below you should begin to see that as you change one side of the triangle the other two see effected as well.
Finally that leads us to the shutter speed on the right side of the triangle. Simply put the shutter speed will decide how much motion we see. Do we want jimmy be a streak of blue as he is running past second base and onto third? Or do we want him crisp and clear seemingly floating in mid air as we catch him between strides? Now what has to happen to the ISO and the F-stop if we increase our shutter speed up to 1\500th of a second? See if you can figure that out by reading the triangle below.