Question

According to the new Cartesian sign convention, all distances in lens problems are measured from:

Options

• The optical centre of the lens

• The top of the object

• The centre of curvature of the first surface

• The principal focus of the lens

Answer 1

In the new Cartesian sign convention used for lenses, all distances (object distance, image distance, and focal length) are measured from the optical centre of the lens. This makes the optical centre the origin for the coordinate system.