How to control the aspherical surface during the optimization

  • 24 March 2022
  • 1 reply

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I had a hard time in controlling the aspherical surface shape on a design found by the hammer optimization (over night, you get it. It’s a better practice to add some constrains before we optimize instead of after the optimization.) for my project. I did some investigation and want to share with you some methods and tools that I found quite useful.

  1. We can use the Q type to optimize, then convert to even asphere if needed for certain reasons.
  2. The tool in Analysis->PAL/Freeform→ Power Pupil/Field Map may help, similarly the surface sag cross section.
  3. Following the second one, we can control these by using POWF and POWP
  4. For mold glass we need something close to sphere, this can be controlled by BFSD
  5. The SDRV and the SCUR can be applied to optimize the plastic lenses to have the desired shape

I may miss some useful tools. Certain methods may not work for certain cases. I would like to know what you think about these methods and do you have other ways to achieve this?

1 reply

Userlevel 5
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I would like to quote the comments from Mark:

I think the points you raise in that article are all very good. I wouldn’t blame the Hamme roptimizer though...its job is to lower the merit function, and that is all it does. Basically you always need to add some kind of constraint to stop the asphere from becoming too wild, or too rapidly changing for manufacture. SCUR and SDRV are all good operands to add to limit the degree of asphericity. The FTGT/LT operands are useful for constraining surfaces which do not have their minimum or maximum thickness at the center or edge, but at some intermediate zone.

Check out the user manual at The Optimize Tab (sequential ui mode) > Automatic Optimization Group > Merit Function Editor (automatic optimization group) > Optimization Operands by Category > Constraints on Lens Data for a listing of all the operands that can be useful to constrain aspheric surfaces.