These 3-element Kellners offer amateurs an excellent alternative to expensive oculars. The lenses are carefully polished from quality optical glass to ensure sharpness. All five kellners are fully coated with an anti-reflection material to maximize light transmission and improve image contrast. Focus length available at 6.3mm, 10mm, 12.5mm, 17mm, 25mm. Apparent Field of View is 50 degrees.