The effect of the atmosphere in making terrestrial objects appear higher than they are, or otherwise distorted; a deflection or distortion of this…

Astronomy. The lowering of the apparent position of a star in the sky as a result of atmospheric effects. Obsolete. rare.

an optical effect, caused by atmospheric distortion, which renders distant objects hazy or discoloured, frequently with a blue tint; the simulation…

Optics. The apparent enlargement or extension of the edges of an object strongly illuminated, when seen against a dark ground.

An optical appearance or counterpart of an object seen double in certain circumstances, esp. as a result of an affection of the eyes like diplopia.

(see quot. 1953).

a form of optical distortion in which straight lines along the edge of a screen, lens, etc., bulge towards the centre; cf. barrel distortion n. at…

attributive. Designating or relating to (a figure illustrating) an optical illusion in which the two ends of a straight line whose central portion is…

An optical illusion in which two transversely placed parallel bars of equal length, or any two figures of equal size, appear unequal when situated…

Distortion of shape caused (or resembling that caused) by centripetal contraction; esp. = pincushion distortion n. at pincushion, n. compounds 2.

the tendency of the human eye, in a featureless visual field, to focus to a distance of only 1–2 metres.

= pincushioning, n. Also: an instance of this.

The Müller-Lyer illusion.