rays travel at shallow angles with respect to the optical axis, so that $\sin\theta\approx\theta$ , $\tan\theta\approx\theta$ , and $\cos\theta\approx 1$ . Aperture effects are ignored: rays that do not pass through the aperture stop of the system are not considered in the discussion below.

Focal points and planes

The front focal point of an optical system, by definition, has the property that any ray that passes through it will emerge from the system

1.Previous
3.Next