Question

write the sign convention used in Optics

Answer 1

sign convention used in optics is relatively simple..
if the object is in left to the pole, its magnitude will be written in negative, if it is placed on the right hand side, magnitude is positive...
   
Above the pole will lead to a positive magnitude while below it will be negative.
If the magnitude of power is negative, the lens used is convex, otherwise, it is concave.
If power is 0, it means that focal length is infinity.