The rule of thirds is one of the most basic composition used inphotography. The rule of thirds makes use of a natural tendency of the human eye to be more strongly drawn towards certain parts of an image.
The rule of thirds is an imaginary grid drawn over an image to break it into nine equal parts The four points where these lines intersect are the strongest focal points. The lines themselves are the second strongest focal points.
To use the rule of thirds you need to imagine the grid on all of your images as you set them up in your viewfinder. If you have an autofocus camera You can use the autofocus points as references to help you imaging the grid. With a little practice you will be able to effectively imagine the grid placement as you shoot.
Which point or line you place your subject on does matter. While any of the points/lines will add emphasis to your subject, some are stronger than others.When an object is alone in an image, the strongest position is the left hand line.
When a subject is not alone there is a hierarchy of image strength. The subject in the foreground will naturally have more strength than the subject in the background. However, the rule of thirds placement can emphasize or reduce this strength. The bottom right point is the strongest for multiple subjects and the upper left point is the weakest. This theory is often used in movies to convey the emotional dominance of one character over another. Placing a background subject on the right and the foreground subject on the left will confuse the eye and lead to confusion in the viewer about which subject is dominant. This technique is very useful for emotionally-charged images.
While most good portraits appear to be simply a centered torso they are following the rule of thirds. In the case of single portraits, the subject's eyes are placed along the top rule of third line. In multiple subject portraits the subject faces are placed on the rule of thirds lines. This is why a multiple-row posing generally works better than a one-row posing.
