As in eyepieces made by Televue.
If I have read correctly, the range in mm of focal length is:- 2.5, 3.5, 5, 7, 9, 11, 12, 13, 16, 17, 20, 22, 26, 31.
Surely the differences between, say, 11mm, 12mm and 13mm are so small I cannot see why there needs to be all three? Why a 16mm and a 17mm?
Am I missing something here?
Eric
