Sky-Watcher 70° Parfocal Eyepiece Series · 1.25-inch/2-inch Dual Interface · Twist-up Eyecup · FMC Multi-layer Broadband Coating 
 Sky-Watcher 1.25-inch/2-inch Dual Interface
5MM / 8MM / 13MM / 17MM feature 1.25-inch and 2-inch dual interfaces, while 22MM features a 2-inch interface. 
 Sky-Watcher FMC Multi-layer Broadband Coating
8 lenses & 6 lenses, multi-layer broadband coating increases light transmission, making imaging sharper and colors richer. 
 Product Name: 70° 5MM, 70° 8MM, 70° 13MM, 70° 17MM, 70° 22MM
Product Focal Length: 5MM, 8MM, 13MM, 17MM, 22MM
Product Type: Parfocal Eyepiece (for all models)
Field of View Angle: 70° (for all models)
Eye Relief: 16MM (for all models)
Number of Lenses: 8 pieces, 8 pieces, 8 pieces, 8 pieces, 6 pieces
Lens Coating: FMC Multi-layer Coating (for all models)
Interface Size: 1.25-inch/2-inch, 1.25-inch/2-inch, 1.25-inch/2-inch, 1.25-inch/2-inch, 2-inch
Product Material: Metal + Outer Rubber (for all models)
 Twist-up Eyecup: 6MM (for all models)
*Manual measurement has an error of 1-2MM, subject to actual receipt. 
 70° Parfocal Eyepiece Series
What is parfocal? It means that when observing under a microscope, after the image is clear with an objective lens of a certain magnification, the image should also be basically clear when switching to an objective lens of another magnification (but there are slight deviations when used on different telescopes, and some need minor adjustments).