Please check out [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=121.0]Lens (thick lens) and Mirror[/url] for large size thick lens.
You are interested in [quote]interaction of light with small sferical objets. It would be great for me to use this applet with mirrors that are convex and adjustable in hight (small, medium and big circles).[/quote]
I did not fully understand what you really want.
Could you explained it in more detail? May be includeing a simple drawing/image (you can attach image).