What's it about?
The optical axis of a spherical lens is the axis passing through the two centers of curvature of the optical surfaces. It is such a simple thing to describe. However, detecting where the axis is and positioning it can be as complex as the definition is simple. Make one or both of the surfaces aspheric and it gets even harder.
This presentation seeks to describe some definitions and detail the parameters used in specifying centration of a lens. These parameters are the same ones used in today's optical design softwares. Next, the means used to check the location of the optical axis and then position it will be described. Lastly, there will be examples showing how design specifications are interpreted on the shop floor...