1. The problem statement, all variables and given/known data Hello! I need to find a local linear increase in the field of the lens. I have Listing of Field Curvature Data. It contains vectors of - Y height, Tan Shift, Sag Shift, Real Height, Ref. Height, Distortion. I can not understand how these data get what I need. 2. Relevant equations Local linear increase in the field of the lens is the ratio of the size of a small object (in the limit of the size tends to zero) located at any distance from the lens center (in this case, the axis Y) to its size in the middle of the field. 3. The attempt at a solution Real Height/Ref. Height ratio is close to Distortion, but not equal, may be it is answer?