Docter is a company that was once part of the Zeiss corporation........I think it was WWII that made them split, and now Zeiss has increased production, while Docter Optics still makes VERY GOOD/GREAT optics they have not used very good marketing techniques (IMO). They have a new type of lens called an a-sperical lens, that does something special, just not sure what............go to their website and you can read about it there.......

Need to know anything else??