What's it about?
This paper defines in detail the parameters used in specifying centration of a lens and techniques used to check location of and position the optical axis. Examples are given of how design specifications are interpreted on the shop floor.
1. PARAMETERS TO SPECIFY CENTRATION OF A LENS
Contained in any spherical lens, there are two primary axes of interest when talking about centration. The optical axis is the axis passing through the two centers of curvature of the optical surfaces. The mechanical axis passes through the physical center of the lens in a direction parallel to the edge diameter. In a perfectly centered lens, these two axes are concurrent and coincidental, superimposed on each other.
Centration errors arise by deviation from perfect, and errors cause deviation in incoming light rays1. One axis may be displaced yet still parallel from the other. This is known as decenter, with the distance between the two axes quantifying this decenter. The other condition, when the two axes become nonparallel to each other, is known as wedge...