Hi,
it really depends what you need to do: Zemax is a rather capable and comprehensive software but for basic design and optimization is a bit of overkilling. I have a license for OSLO (Lambda Research): the program is ok but a bit outdated, structure similar to Zemax. There is also an EDU version, limited to 10 surfaces, which you can use for free. Another free alternative is KDP2 http://www.ecalculations.com It is rather capable, but I did not use it for any serious design.