Large discipline binoculars typically make the most of some type of Erfle configuration, patented in 1921. These have five or six features in 3 teams. The groups may be two achromatic doublets with a double convex singlet amongst them or may possibly all be achromatic doublets. These have an http://binoculars96418.theideasblog.com/12838501/the-ultimate-guide-to-binoculars