What does Ed mean on Olympus lenses?

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Tags

1. #chromatic
2. #quality
3. #entire
4. #effectively
5. #across
6. #aberration
7. #still
8. #lighter
9. #dispersion
10. #element
11. #image
12. #return
13. #smaller
14. #glass
15. #excellent
16. #results
17. #lenses
18. #extra
19. #optimal
20. #reduce
21. #zuiko