There are a number of different file types which are used by ZEMAX, but perhaps the most commonly misunderstood functionality/purpose of these files is that of the configuration (.CFG) and session (.SES) files.  Each serve a specific purpose, and will be explained in detail in the following paragraphs of this article.



The .SES file extension, or the “session” file, are those which define the display configuration and open windows and settings for each saved .ZMX lens file.  By default, whenever you save your lens file, ZEMAX also creates a session file with the same filename as the lens file, but just a different extension:  .SES.  Then, the next time the lens file is opened, all of the analysis windows and editors appear in the exact same location as they were when the file was saved.  In addition, the session files contain the setting information for each of these open analysis windows, so the designer may better recall the analysis which was being performed upon last saving the file.

The use and creation of session files may be turned on or off under the File menu within ZEMAX:



If this option is unchecked, then no session file is created upon saving the lens file.  In addition, even if a previously saved lens file has an associating session file, none of the analysis windows will be recalled.

When sending a colleague/customer your lens file, it is often useful to send the session file as well.  This is especially true when sending your file for review to ZEMAX technical support.  By sending your session file along with your ZEMAX file, our support staff can immediately assess the question at hand, and review the appropriate analyses without having to ask for specific setting information.

Throughout the ZEMAX online knowledgebase, sample files are included for download at the end of an article.  Often times, the .ZMX and .SES files are included.  As long as both files reside in the same directory, then upon opening the lens file, the appropriate analysis windows will also be displayed.



In addition to the lens and session files are the configuration files.  Configuration files serve a different, unique purpose from that of the lens and session files, which is discussed on the following page.