Magnifier lens = Double CX lense ?

I am looking for a 4 inch or bigger lense with a 2x or 2.5x like the one RedDevil said is needed for a big MH Bulb. So far i have no luck finding a "magnifier lens" online. Is a magnifier lense is the same as a double convex lense? I need it to be place in front of the bulb. Also, i used a tin foil tape as a reflector, is that good enought? Thank again guy.