Following are the sign conventions for all types of mirrors, lenses, spherical refracting surfaces
1. All distances are measured from the pole of the mirror.
2. Distances measured in the direction of incident ray are +ve & that measured in the opposite direction are –
3. Distances measured upward to the principle axis are +ve & that measured downward are –
Using the image formation rules, sign conventions & simple laws of geometry we can prove the relation between u, v, f, m, I, O, f, R & P.
Don’t put the sign for the quantity to be calculated.