focus pay attention listen draw

Moved up and down to bring the specimen in focus.

---Co0lets24

Spot lighting can be used to draw attention to art pieces.

Draw several circles from the under ground point called focus.Color it by red and blue alternatively.One is for primary and the next one is for secondary.The gap at focus between primary and secondary should be very close and as the distance goes beyond focus the gap between primary and secondary should be more.This difference represents the speed difference of those two waves.

Simply put, light rays do not focus light because the focus is on the wrong side of the lens, with respect to the incoming light. If you draw the ray diagram you will see that the parallel rays transmitted may appear to be coming from a focus. This is what they mean by virtual.