Meniscus lenses are often employed in conjunction with another lens to produce an optical system having either a longer or shorter focal length than the original lens. We specialize in the production of medium to large-size series of custom lenses with exacting tolerances, high grade surface finish and difficult coatings. Please send us your specification or drawing and we will be happy to return a quotation ASAP. Our average response time is within 24 hours. Specifications: 1) Diameter: ?25.4 - 254mm 2) Material: BK7 (K9) 3) Surface quality: up to 60-40 S& 4) Surface accuracy: up to ?/4 5) Clear aperture: > 90% 6) Diameter tolerance: +0.0 / -(0.1 - 0.2) mm (depends on dimension) 7) Focal length tolerance: