| Doublet lenses are used to produce a higher quality image than singlet lenses of which they easily out perform, even in monochromatic light. Doublet lenses are made up of two different types of glass, a flint and crown glass. These doublet lenses are designed to correct spherical aberration and coma as well as for chromatic aberration. Freedom from spherical aberration means that the focal length is independent of aperture. Doublet lenses performance and usages depend on the relative aperture. All but the largest apertures are diffraction-limited on axis and give excellent imaging over a small field (say 5°) as required for microscopes etc. Negative doublets are commonly inserted between an objective and its image to increase the tube length (as in microscopy) or magnification (as in astronomy) they are therefore optimised for these conditions of 2x. Specifications: | Typical Material: | Flint (SF2) and Crown (BK7) | | Diameter: | +0.0 / -0.10mm | | Centring Accuracy: | < 0.1mm (F.L ≤ 40mm) < 2.5mrad (F.L > 40mm) | | Focal Length: | ± 0.1% (≤ 10mm) ± 1% (>10mm) | | Surface Quality: | <40-20 scratch/dig | Coating: Flint element AR coated for high index @ 550nm (AV7) Crown element AR coated for low index @ 550nm (AV5) Options available: >> Mounting (circular lenses only)>> Special AR coating>> Cutting to special sizes>> Stock lenses can be edged to smaller diameters | 
Doublet Lenses - Negative Type
