. State the sign convention to measure the distances for a lens
State the sign convention to measure the distances for a lens.
The axis along which the distances are measured is called as the principal axis. These distances are measured from the optical centre of the lens.
The distances measured in the same direction as that of incident light are taken as positive
The distances measured against the direction of incident light are taken as negative
The distances measured upward and perpendicular to the principal axis are taken as positive
The distances measured downwards and perpendicular to principal axis is taken as negative
The focal length of the convex lens is taken as positive and that of concave lens is taken as negative