The rule of thirds is a "rule of thumb" or guideline which applies to the process of composing visual images such as designs, films, painting, and photographers. The guideline proposes that an image should be imagined as divided into nine equal parts by two equally spaced horizontal lines and two equally spaced vertical lines, and that important compositional elements should be placed along these lines or their intersections.
The rule of thirds is applied by aligning a subject with the guide lines and their intersection points, placing the horizon on the top or bottom line, or allowing linear features in the image to flow from section to section. The main reason for observing the rule of thirds is to discourage placement of the subject at the center, or prevent a horizon from appearing to divide the picture in half.
Leading Lines
Leading line paves an easy path for the eye to follow through different elements of a photo. Usually they start at the bottom of the frame and guide the eye upwards and inwards, from the foreground of the image to the background, typically leading toward the main subject.
The easiest place to find a leading line is on a road. Roadways are inherently leading because they go somewhere, give us a feeling of motion, and the lines often point so far inwards that they reach a vanishing point – the place where two or more lines converge into theoretical infinity.
When leading lines, such as roads, connect the foreground to the background of a scene, they help to create depth and dimensionality which draws the viewer into the image.
Depth Of Field
In optics, particularly as it relates to film and photography, depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.
In some cases, it may be desirable to have the entire image sharp, and a large DOF is appropriate. In other cases, a small DOF may be more effective, emphasizing the subject while de-emphasizing the foreground and background. In cinematography, a large DOF is often called deep focus, and a small DOF is often called shallow focus.
