DESC: If you are 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 this series with the finer points in mind so you, the user, can benefitfrom the features that make this series unique. The Omni is a 4 -element premium symmetrical Plossl optical design. Features include blackened lens edges to minimize internal reflection and maximize contrast, multi-layer coating group oneach lens surface to maximize light transmission and contrast, and each Omni goes through a two-step anodizing process to prevent reflection from the top eyepiece barrel, unlike most other manufactures who use reflective surfaces. Threaded barrels accept 1-1/4 Celestron thread-in filters.