Baader Hyperion Finetuning-Ring, 14 mm

Focal lengths Fine Tuning for Hyperion eyepieces (all focal lengths)
Optical path length 14mm
Spacer rings fit between the negative lens and the 2 "barrel, so that it matches the respective eyepiece to your needs.
The 13 mm eyepiece transform e.g. no loss of quality in a 9- or 11 mm eyepiece.