It is not only this distortion that need to be compensated for in the lens design as even for two objects of the same size, with the nearer one distance "a" and the other one at "b", the images perspective size will differ less as the distance becomes greater. For objects at distances x and y, the nearer appears twice as large as the further, but at distances 10m and 11m respectively, their difference is 10 per cent which is noticeable, get further away and this becomes a real issue. But for the average head with a distance of 75 mm from the ears to the tip of the nose, a viewpoint at 2 m gives the nose on a scale only 5 per cent larger appearance than the ears, which is acceptable. Small children are exceptional in this rule.
For more information read sections on Optical Design
, Chromatic Errors
, Lens Flare
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