18mm Focal Length 52 Apparent Angle of View 1.25″ Diameter Barrel True High-Transmission Multi-Coatings 4-Element/2-Group Lens Design Produces Low Power on Most OTAs Winged Rubber Eyecup Parfocal with All Baader Ortho Eyepieces Employing a classic orthoscopic design and engineered primarily for planetary viewing, the Alpine Astronomical Baader 18mm Classic Ortho Eyepiece makes an ideal addition to your observational kit. With a generous 52 apparent angle of view, it produces a relatively low magnification on most optical tube assemblies (OTAs). This model is parfocal with other Ortho eyepieces, which means there is little to no need to refocus when changing eyepieces within the Ortho line. It features a 4-element/2-group lens design with a triplet-element and one plano-convex eye lens, so there are only four glass-air-surfaces to limit internal diffraction and limit light loss. True High-Transmission (HT) multi-coatings on all glass-air-surfaces yield brilliant images while virtually eliminating internal reflections, that when paired with the lens design, delivers a pure-white image with improved sharpness and contrast. The interior of the anodized housing is blackened to suppress stray light, and has machined threads to accept most standard 1.25″ filters. It is made with a standard 1.25″ barrel so it is compatible with the most popular-sized holders and accessories. Alpine outfitted it with a winged eyecup to block stray terrestrial light to improve brightness and contrast, while helping to eliminate distractions.