Is there a difference? Is there any advantage of one over the other?
[QUOTE=ScoutMan;1508570]Is there a difference? Is there any advantage of one over the other?[/QUOTE]
ED is Extra-low Dispersion, whereas HD is High Definition.
Further details of exactly what characteristics each has would probably be best found from the relevent manufacturer's websites.
Neither of these marketing terms describes an actual glass type. The family of "ED" glass types consists of a number of different glasses with Abbe numbers between about 80 and 95. All have the potential to reduce longitudinal CA compared to a conventional crown and flint achromat, but only if they are properly matched with other types. The greatest potential for CA reduction comes from the types with the highest Abbe numbers. The binocular manufacturers seldom reveal what "ED" glass type they use and never reveal the matching types.