It is often times very convenient to analyze rays with specific qualities in order to assess the design and make the necessary adjustments to improve its performance.  The filter string is a convenient tool in ZEMAX which allows the definition of a "test" that rays must pass before they are drawn or displayed.

Filter strings can be used to perform a full-optomechanical assessment of stray light, and will consider reflections, scattering, coatings; etc to both mechanical and optical components.

Filter strings may be applied to the initial Ray Trace/Detector Control dialog, Layouts, Detector Viewers, and within the Ray Database Viewer.  Each of these analysis tools, in conjunction with the filter string, may be used in many different ways to isolate rays with specific properties.  There are many filter string flags which are built into ZEMAX, and with the support of logical flags, the possibilities are endless.

REFERENCES

ZEMAX Optical Design Program User's Guide, ZEMAX Development Corporation