OK, some of you may know I am currently searching for a camera whether it being film or digital. I know that the dSLR-like cameras with fixed lenses have their lenses measured by 'X' eg. 3x, 4x, 10x, 12x etc. But the lenses you can buy for a DSLR are measured in mm eg. 28mm-55mm etc. What is the equivalent x to mm?