Stereopsis

Hammerhead sharks have widely separated eyes.

Stereopsis is the ability of the brain to 'stitch' two images with slightly different geometry into a full three dimensional view. The effect demands high visual acuity (image quality) which requires high light levels. The ability is lost from early evening as the light fades. 

In good light most people can, with a little thought, locate the apparent depth (or length) of a fish tank full of water to within ±1 cm and the position of a real image of a ceiling light reflected by the bottom surface of a large convex lens to within ±1 mm.

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