TeleVue - Dioptrix Correcting Lens

Your telescope's focuser is used to compensate for your near- or far
-sightedness; DIOPTRX™ compensates for your astigmatism. These units
attach and lock onto the tops of over 20 long eye-relief Tele Vue eyepieces
to achieve the sharpest full-field viewing possible. DIOPTRX™ models
are available in .25 diopter steps, from .25 up to 2½ diopters, and are
rotatable for tuning to the best orientation. A series of engraved letters
on the barrel helps to monitor orientation. Simply choose the
DIOPTRX™ model that matches your eyeglass prescription for
astigmatism. All lenses are multi-coated glass in anodized aluminum
housings with rubber eyeguards.