A photograph is a two dimensional representation so depth must be inferred using visual clues such as relative size and perspective. Objects which are closer to us appear larger than similar objects placed further away and our visual sensory processing uses this to reach conclusions about images. Where lines converge towards a vanishing pont the impression of depth is created within the frame. The actual vanishing point need not be within the frame itself.
Bridges often have useful ‘leading lines’ as in the above example. Several lines are clearly converging towards an in-frame vanishing point – the parapet walls, the kerb and the shadow. The road continues where the bridge itself ends, leading the viewer’s eye to the distance. This is a ‘pointless’ convergence in the sense that there is no object of interest at the distal end.
In this example the lines do converge on something visible, leading the eye into the narrow streets of the town. The cobblestones, being apparently larger in the foreground and becoming progressively smaller, give additional cues about depth. The more pronounced the difference between the lines at the beginning compared to the end, the greater the suggestion of depth. If the lines begin close to the edge of the frame the effect is further enhanced.
In this image the effect is very pronounced because the line starts at the frame edge and travels through, almost to the upper edge. Again, there are several distinct lines to be seen in the concrete edges and the boundary of sea and rock armour. Even the horizon leads to the vanishing point. The wide angle lens (24mm equiv) emphasises the impression and appears to have bent the horizon as well.