The (mostly) parallel rays of such instruments tends to cast hard shadows, unlike soft light sources.

A perfect parabolic mirror will bring parallel rays to a focus at a single point.

Different acceptance angles may then be determined for parallel rays or for sunlight.

Distinct lines carrying limiting parallel rays do not meet.

This corresponds to the point of focus for parallel rays.

This eye, when not using accommodation, cannot focus parallel rays of light (light from distant objects) on the retina.

A nephroid may be viewed as a caustic of a circle for parallel rays.

A parallel beam is described as a group of straight and parallel 'rays'.

In a hyperbolic plane, one can define an ideal point or end to be an equivalence class of parallel rays.

For parallel rays, such as those coming from a very distant object, a parabolic reflector can do a better job.