What's it about?

This paper will list some items to consider during the initial lens design phase that will expedite later fabrication, with items applicable to any lens type.


The designer builds a lens design to meet performance specifications, and the specifications of each lens (material, radii, diameter, thickness, surface quality, and centration) receive a tolerance. The tolerance assigned has direct influence on the ultimate performance of the lens system1 while the restrictiveness of the assigned tolerances has a direct influence on the cost of the lens or even if the lens can be made2.


The fabricator interrogates every specification shown on the drawing, placing each item in one of two categories, reference and reportable. Each reportable item has to be measured, certified, or both, and it takes time to collect, record, manage, and archive this data. This effects price. Material certifications, custom line reads or homogeneity, take time and protract delivery3. While lens design software contains inputs for many specifications, apply only those vital to lens performance.

It is a sensible practice to learn from the lens fabricator what specifications are easily achieved and which approach or exceed the impossible. There are plenty of situations where “take my word for it” is not acceptable, but there are some where it is. For example, most conventionally polished spherical lenses have surface roughnesses well under 20 Å RMS4, so adding a specification for 50 Å adds cost, takes time to prove what the fabricator already knows, and, for most visible and infrared applications, is unnecessary5...