If youre looking to move up to a higher quality eyepiece the omni series provides more enhanced features in a wider selection of focal lengths celestron designed the series with the finer points in mind so you the user can benefit from the features that make this series uniquethe 4mm high power omni eyepiece is a 4 element premium symmetrical plossl optical design features include blackened lens edges to minimise internal reflection and maximise contrast multi layer coating group on each