Eyepiece Orion Sirius Plossl 20mm Orion Telescopes & Binoculars · Sirius Plossl 20mm Key specifications Focal length20 mm Apparent FOV52 ° Barrel size1.25" All specifications Elements4 About 20mm 52-degree Plossl eyepiece; Orion's standard 4-element Plossl line.