Exercise 2.1 (supplementary) – a change of perspective?

An extract from the centre of a 9mm (18mm equivalent) view is compared with a 149mm (298mm equivalent) view.

The extract is distorted as a result of the rectilinear geometry of the lens. In keeping straight lines straight, there is a ‘stretching’ toward the corners. Ironically, a fisheye wide-angle would give lesser distortion in small detail areas.

The extract appears unsharp because it is over-magnified and the pixels ‘smudged’ in the enlargement algorithm. There is also some exaggerated chromatic aberration. These are very good reasons for using an appropriate focal length, rather than trying to enlarge from a wider image.

The object of the exercise is to demonstrate that there is no change of perspective between the two views. This can be most easily seen by the relationships between (a) the rear bumper of the black car and the wheel of the silver car, (b) the windscreen pillar of the silver car and the rear side window of the front car and (c) the right-hand signboards and the tree trunk.

Changing the focal length changes the angle of view but not the perspective relationships between picture elements.


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