The celestron omni 4mm eyepiece is a 4 element premium symmetrical plossl optical design which determines your telescopes magnification and can give you a wider field of view the features of this eyepiece include lens edges to minimise internal reflection and maximise contrast and fold down rubber eye cups for comfort of use rubberised grips come as standard as wellrrthe eyepiece has multi layer coating group on each lens surface to maximise light transmission and contrast and each omn