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N-SF11 Plano-Concave Lenses, Uncoated
These Plano-Concave lenses, which are fabricated from N-SF11 glass, are uncoated. N-SF11 glass, a RoHS complient version of SF11, is most commonly used in harsh environments since it is inert to biological degradation and resistant to naturally encountered chemicals, alkalis, and acids. With an uncoated wavelength range of 420 nm - 2.3 μm, N-SF11 also offers a usage range that is slightly shifted to the red compared to N-BK7, which is our RoHS-compliant BK7 glass and has an uncoated wavelength range of 350 nm - 2.0 μm. Since N-SF11 glass has a lower Abbe Number than N-BK7 glass (25.76 compared to 64.17), it is associated with more dispersion.
Like all plano-concave lenses, these lenses have negative focal lengths and can be used to diverge collimated beams. In this case, the curved surface of the lens should face the source to minimize spherical aberration. In addition, they can be employed to offset the effects of spherical aberration caused by other lenses in an optical system.
Below is the measured transmission for a 10 mm thick uncoated sample of N-SF11 using normal incident light. Each lens can be purchased uncoated or with our -A (350 - 700 nm), -B (650 - 1050 nm), or -C (1050 - 1700 nm) antireflection coating.
Mounting High-Curvature Optics
Thorlabs' retaining rings are used to secure unmounted optics within lens tubes or optic mounts. These rings are secured in position using a compatible spanner wrench. For flat or low-curvature optics, standard retaining rings manufactured from anodized aluminum are available from Ø5 mm to Ø4". For high-curvature optics, extra-thick retaining rings are available in Ø1/2", Ø1", and Ø2" sizes.
Extra-thick retaining rings offer several features that aid in mounting high-curvature optics such as aspheric lenses, short-focal-length plano-convex lenses, and condenser lenses. As shown in the animation to the right, the guide flange of the spanner wrench will collide with the surface of high-curvature lenses when using a standard retaining ring, potentially scratching the optic. This contact also creates a gap between the spanner wrench and retaining ring, preventing the ring from tightening correctly. Extra-thick retaining rings provide the necessary clearance for the spanner wrench to secure the lens without coming into contact with the optic surface.