When introducing compensators to your tolerancing analysis, you can either choose “Optimize All” or “Paraxial Focus”, found in the “Comp” drop down menu.

Paraxial Focus compensation is a very handy tool that makes several assumptions to expedite the tolerancing analysis. It ignores any compensators you have defined and uses only the back focus. The last thickness is then split into two surfaces: the first uses a paraxial image solve that is automatically updated to locate the paraxial image plane, and the second is a minor correction that adjusts for the real image location. This isn’t a complete optimization of the back focus, but rather it maintains the amount of defocus from the nominal design. This method is accurate for systems that are rotationally symmetric and only use back focus as a compensator; however, when there are additional compensators, “Optimize All” will clearly give a more accurate result. By avoiding the time-consuming cycles of optimization, “Paraxial Focus” is a useful tool that can speed up your tolerancing analysis and provide accurate results when used with a system that is well defined by paraxial rays and lacks additional compensators.