Controlling Quality in Off-Axis Parabolas (k, f, theta, OAD)


Controlling quality of off-axis parabolic mirrors requires tolerances that are both traceable to performance and verifiable by measurement. Primary aspheric parameters for off-axis parabolic (OAP) mirrors, include the conic constant (k), focal length (f), off-axis angle (OAA or“θ”) and off-axis distance (OAD). We defined these in our application note, “Specifying the Geometry of an Off-Axis Parabolic Mirror”.

Getting the OAP configuration right may be the first step, but determining appropriate tolerances is next. What then are reasonable assumptions for tolerances on these key parameters and how are they measured? Intuition might suggest applying tolerances of angle and distance as one would for a spherical optic. However, because the primary design parameters in an asphere are interdependent, it is not always practical or even possible to verify these quantities by independent measurement as you may for a sphere or flat optic. Therefore, if something so fundamental as focal length or off-axis angle cannot easily be verified, how can the quality be guaranteed? This application note explains how AOS addresses this fundamental question. Our answer may surprise you.

Download the full pdf technical note here. 

Posted: February 16, 2021