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8. Distortion (2 Viewers)

If there are any straight lines near the edge of the image that appear somewhat curved it is referred to as distortion. Barrel distortion bends the lines outwards; with Pincushion distortion lines are bent inwards.

If a pair of binoculars is absolutely distortion-free objects at the edge of the image field appear somewhat smaller than objects in the centre.

When the user pans some models of binoculars there is an impression of objects moving from the side of the image, expanding in the centre, and then getting smaller on the other side of the image. It resembles the appearance of a rotating globe, thus it is known as “the rolling globe effect“ or “rolling ball”.

To counteract this, many binoculars are deliberately designed to have a controlled amount of pincushion distortion. This causes magnification to increase towards the edge, and while this means straight lines at the edge of the image are bowed inwards, and this can be somewhat annoying, there is a steadier and more natural image when the binoculars are panned. Because objects consisting mainly of straight lines rarely occur in nature, except perhaps in pine forests planted by man, all ZEISS binoculars include this proven and important minor nominal distortion, to enhance viewing comfort in dynamic viewing situations.

distortion.png

Left: No distortion. Right: Nominal pincushion distortion.
 

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