Summary
Description 
Figure illustrates use of positive & negative curvatures for the surfaces of a lens.
Think of the principle axis as being a real number line, with the midplane marking the origin of the axis. Light rays travel in the positive direction. IF the center of curvature – for either surface – lies in the negative region, then the curvature is negative, R < 0. IF the center of curvature – for either surface – lies in the positive region, then the curvature is positive, R > 0. 
Date  
Source  Own work 
Author  Erik LongLeaf 
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