# Convex lens – object at F

An object at F is an object at one principal focal length away from the convex lens.

We use the two most important rules of ray diagrams

1. From the object, pass a parallel line through the principal focal point.
2. From the object, pass a ray line through the centre of the convex lens.

The refracted rays travel parallel with each other. You cannot see an image by looking or using a sheet of paper.

At F, no image