03.05 Diagonal lines

Diagonals have more freedom of direction than the Cartesian axes - verticals and horizontals - because they are released from alignment with the image frame.

1. Diagonals are dynamic
Where Cartesians have a sense of stability or being supported against the effects of gravity, diagonals have the opposite - of falling under gravity. Diagonals thus have greater dynamism associated with a feeling of speed.

2. Diagonals convey depth
Diagonals predominate the man-made environments as a result of linear perspective: non-centred straight lines or edges receding into the distance appear as diagonal lines.

Diagonal lines are thus important elements for their ability to direct a viewer's eye: we are programmed to follow the line of a diagonal because we use it for depth determination, and for gauging the speed of movement of an edge falling under the effects of gravity.

As seen in frame dynamics, diagonals interact with the image frame to create visual tension. For single diagonals, visual tension increases proportionately with the angle between the diagonal and the long side of the frame up to a maximum of 45 degrees. For multiple diagonals, visual tension:

• has more 'weight' in the case parallel diagonals because the tension created by one diagonal with the image frame, is reiterated by identical tension from the other diagonals.
• is strongest when there are multiple diagonals at different angles, where there is tension created between the diagonals as well as the image frame.

In practice, parallel diagonals can be achieved from high vantage points using the compressing effect of a telephoto lens. Multiple convergent diagonals can be achieved in low or close positions with a wide-angle lens.