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You show two versions of Andrea Mantegna's The Dead Christ ("Brush-off for Hockney idea", THES , August 23). Christopher Tyler's has the head at a distance beyond the feet in contrast to Mantegna's original with a large head compared with the feet.

If a television camera lens is just behind the wickets at one end of a cricket pitch, the stumps at the far end look smaller than the near ones.

But if the camera lens, which cannot by itself change relative sizes of images, is on the boundary behind the wicket, both sets of stumps, near and far, will seem the same height. This is because an extra 22 yards of pitch to the distant wicket is unimportant from the boundary viewpoint.

Zooming in has no effect on perspective, whereas moving the camera lens towards the subject does. This inclines me to think that Mantegna's view, with its "giant" head, indicates the subject was seen from a distant viewpoint.

John Little
Bishopriggs, Glasgow.