Question

state the new cartesian sign convention for lenses​

Answer 1

according to the convention the focal length of a convex lens is positive. and that of a concave lens is negative. according to the new Cartesian sign conventions the optical centre o of the lensis taken as the origin. the principal axis of the lensis taken as the x axis X - X of the coordinate system.

Answer 2

1).all the distance are measured from pole of the lens
2).the distance measured upward to the principal axis are taken as positive.
3).the distance measured in the direction as that of incident ray are taken as positive