OSLO, Optics Software for Layout and Optimization.
The version OSLO-EDU (for education) can be downloaded for free. But compared with other software demos or free version, OSLO-EDU still contains a lot of features which enables you to really work with it. Good and extensive introductions, manuals and examples exist and will help you to operate the software. But as with every software, you have to spend first a little bit time to learn it, depending what you want to design. OSLO is provided by the company Lambda Research Corporation. The link for the download page you can find here:
Download OSLO-EDU
on the same page you can also download 2 manuals. I hope for smaller optical design tasks this software will help you.
Lambda Research Corporation
OSLO Wikipedia
Code V
Zemax