I don’t like to talk about “rules”. I prefer to call them just advices. In fact following rules in photography means to understand nothing about it!
Anyway everybody calls them “rules” so let’s keep the traditional name.
These rules are based on the The Golden Ratio. It’s a special proportion that exists everywhere in nature. For some reason, it’s related to us as living beings in this universe and it affects the way we interact with things.
Rule of Thirds
This rule is more about composition. It has a strong relationship about how humans perceive reality and how humans read visual information.
You just have to divide the frame in three parts horizontally and vertically. So we will have three zones and 4 intersection points.
Try to place the objects of interest in the intersection lines and avoid to center the object in the middle of the image.
Of course it depends, for example, in this picture I cropped it to put the main subject (it was me…) in the middle of the frame. Why? Because the main subject of this picture is not related to the sharpness of the image but to the whole situation that shows a man fighting the wind with his bicycle.
One more scenario where the Rule of Thirds is applicable is in landscapes, where the horizon line plays an important role in the composition. Just try to avoid the horizon line to divide the image in two perfect parts. Just place the horizon line in the upper third or the bottom third, depending on which part of the image you want to give more emphasis. For example, if it is the sky, put the horizon line in the first third from the bottom.
Of course there are exceptions, for example in this picture I preferred to leave the horizon line just in the middle because in this picture the important part is just the horizon!
In this case we use the zone indicated by the following image. The important part of the image will reside in the zone delimited by those lines.
For example these pictures can illustrate these rules:
One more application of the golden number is an spiral. The one I draw in the picture is not perfect, but it renders the idea.
It’s not necessary that the object takes the whole picture. The important thing is that the composition makes the eye move to the center of what you want to show.
For example in this picture, your eyes will go immediately to the faucet. Okay, it’s the biggest object in the composition, but if I would like to take the faucet in the middle of the frame, the eyes wouldn’t point directly to the faucet as in this case:
There are more rules, these are the basic ones and the possibilities to play with proportions and discover new properties are infinite… So let’s try and play :)