Inside the Focal Point Is Not a Mistake

You'll learnwhere a principal ray starts and bends, how the thin-lens equation is actually solved, and why an object inside the focal length is a magnifying glass rather than a broken problem.

An arrow stands in front of a converging lens, and the rays that leave its tip cross again on the far side: an image. Push the arrow inside the focal point and something different, and just as legitimate, happens. Eleven short steps; press Next for each one.

11 STEPS · 6 QUICK CHECKS · START AT THE TIP · INSIDE f IS LEGAL · v2

rays start at the tip · inside the focal point is a magnifying glass

Before you start

What you're looking at

A converging lens on an axis, its focal points ticked, and an object arrow beside it. Rays from the arrow's tip locate the image.

The question

Where does each ray bend, and what happens when the object moves inside the focal point?

Step 1 / 11