FRED imports lens prescriptions from CodeV, Zemax and OSLO either into an existing FRED document or a new FRED document. Most surface types are supported, though in cases where FRED cannot import a surface type a message will be printed to the output window (you may need to scroll up through the output to find errors).
This command can be accessed in the following ways: •Menu > File > Import > Import Optical •Ctrl + Shift + I
Zemax files must be saved in ANSI format rather than UNICODE for proper recognition by FRED. This file format specification is a setting in the Zemax preference menu called "ZMX File Encoding".
Compute apertures from paraxial raytrace If "Compute unassigned apertures from paraxial raytrace" is not checked, then FRED will prompt the user for aperture information (see Import Apertures). When the apertures are computed from the paraxial raytrace, FRED will use the lens aperture specification "Edge with front and back bevels". The bevel size is the difference between the largest and smallest surface apertures of the lens as computed from the paraxial trace. For example, if the paraxial aperture size is 10 mm and the paraxial trace calculates a ray height of 9 mm, then the imported lens would have a 1 mm bevel. Note that the aperture specification, "Edge with front and back bevels" requires the user to change both the surface apertures and bevel apertures from the Advanced Aperture settings on the lens dialog.
Zemax and OSLO assign default apertures to all optical surfaces; CodeV does not. Before writing a *.seq file in CodeV, issue the command SET APE SA to set all surface apertures. If the CodeV model contains surfaces with both aperture and edge specifications, the imported model will contain aperture curves matching these specifications. In this case, the user may notice that rays between the edge and clear aperture are halted from further propagation. Please see the aperture curve collection Help topic. On import, the Aperture Curve Collection algorithm will be set to "Sequential with absorb ==> miss", which Photon Engineering believes is the algorithm most compatible with the CodeV interpretation of apertures. If the user observes that aperture behavior is inconsistent with the expected behavior, they should try toggling the Aperture Curve Collection into one of the other algorithms.
All Zemax glass catalogs pertinent to an imported Zemax prescription must be located in same directory as the Zemax file as FRED does not search the user's disk in an attempt to locate these catalogs. If the catalogs are not found, FRED substitutes a dummy glass with n = 1 for any unknown glasses.
One failure mode related to glass catalogs is a mismatch between the catalog file name and entries on the GCAT line of Zemax files. FRED insists that these entries match exactly, and verification can be made by opening the Zemax file with an editor such as Notepad.
All "dummy" surfaces should be removed from lens prescriptions prior to import. Failure to do so may lead to incorrect interpretation of Lens elements and raytrace warnings related to improper Material assignments and or coincident surfaces.
Zemax multi-configuration and non-sequential FRED does not import multi-configuration or non-sequential Zemax files.
When aspheres are imported, it is possible that both branches of the function will be displayed. Zemax and CodeV check for these branches and select one or the other automatically, but FRED does not. The advanced dot-product trimming specifications on the Aperture tab of a surface dialog can be used to remove any unwanted branches.
In certain configurations, the sign of the diffraction order on imported gratings must be flipped in order to make the raytraces between FRED and Zemax agree. At this time, it is unknown under what scenarios this sign change needs to be made.
The Zemax Paraxial Surface type is supported in the importer but the FRED and Zemax implementations of a paraxial surface when phase information is being tracked (i.e. coherent calculations in FRED) may not be identical. The user bears the responsibility of verifying the intended behavior after import.
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