Yes, multiple versions of OpticStudio may be installed on the same machine for regular use. This can be done by changing the directory for installation. By default, the installer will choose the following as the default location: “C:\Program Files\Zemax OpticStudio”. If this file location is chosen, the installer will overwrite any other versions of OpticStudio you have in that location.

A good strategy is to rename the file destination with the version tagged at the end, as shown:

Once the destination location is chosen, move to the next screen to choose the name of the Start Menu folder. As before, make sure to differentiate the name of the folder from other versions available on your machine.

Note: Multiple versions should be installed oldest to newest. This ensures that you have the latest catalogs available for use.  

I follow up to this old thread to point out an issue with ZOS updates.

Basically, there is a difference between what is actually installed and what Windows “thinks” is installed (or, let’s say, what ZOS installers make Windows think is installed). 

To better explain what I’m saying, here follows some screenshots from an old update, but the same behaviour can be reproduced with the latest version.

1. Install the new version (21.2) by overwriting the older (21.1.2)

2. ProgramsAndFeatures shows two installations, but actually one is present in the OS (because the older have been overwritten).

3. By Uninstalling the old version (21.1.2), actually the new and only version (21.2) is unistalled.

4. Now Zemax is not present in the OS: just few spare files can be found in the Install folder and obviously the Application cannot be found and all links are missing.

Nevertheless, the new version can still be found in ProgramsAndFeatures.

As a result, upon updating, I warmly suggest to either:

• uninstall the previous ZOS version, or
• change installation directory for the update, as Allie pointed out above.