Sign Convention of Lens

Sign Convention of Lens :- Sign convention is a set of rules to set signs for object distance (u), image distance (v), focal length (f), etc. for mathematical analysis of image formation. According to it :-

• Object is always placed to the left of lens.
• All distances are measured from the optical center of the lens.
• Distances measured in the direction of the incident ray are positive and the distances measured in the direction opposite to that of the incident rays are negative.
• Distances measured along y-axis above the principal axis are positive and that measured along y-axis below the principal axis are negative.

Note :-

• Sign convention can be reversed and will still give the correct results.
• Convex lens has positive focal length and concave lens has negative focal length.