Eyepiece Orion Sirius Plossl 17mm Orion Telescopes & Binoculars · Sirius Plossl 17mm Key specifications Focal length17 mm Apparent FOV52 ° Barrel size1.25" All specifications Elements4 About 17mm 52-degree Plossl eyepiece; Orion's standard 4-element Plossl line.