Ethos Focal Length Groups of Three

Why are Tele Vue Ethos eyepieces often recommended in groups of three focal lengths:

21mm, 13mm and 8mm

or

17mm, 10 and 6 mm?

Originally Posted by James Erwin

Why are Tele Vue Ethos eyepieces often recommended in groups of three focal lengths:

21mm, 13mm and 8mm

or

17mm, 10 and 6 mm?

Depends on your scope but of the two groups I'd go with the 17, 10 and 6mm because the 21mm weighs a ton and may cause balance issues and the 10mm tests much better optically on the bench tests than the 13mm.