89-618 25mm Dia. Silicon Aspheric Lens; EFL=50mm; NA=0.25 BBAR 3-5µm

This is the 89-618 model from Edmund Optics, a 25mm diameter Silicon Aspheric Lens with a focal length of 50mm and a numerical aperture of 0.25. The lens is coated with BBAR (Broadband Anti-Reflection) coating, which is effective for wavelengths between 3µm and 5µm.

The lens features a base shape of a circle and is made of silicon, specifically silicon sal vil 1957. The inner radius and outer radius are not specified, suggesting that these parameters are not relevant or are proprietary to the manufacturer. The lens has a thickness of 2.3mm at the edge and 3mm at the center.

The front and back of the lens are coated with edm arcoatedsilicon, providing excellent light transmission and reducing surface reflections. The lens's shape is aspheric, which means it has a non-spherical surface to correct spherical aberration and provide sharper images.

The lens's geometry includes a back focal length of 47.78mm and a clear aperture of 25mm. The lens's design includes a conic constant (k1) of -0.1221946, indicating a mild asphericity. The lens's material has a refractive index of 3.42 at 20°C and a dispersion of 60.

The lens is available for purchase through the Edmund Optics website, and the link provided is valid and indicates that the lens is in stock. This lens is suitable for applications that require a high-quality, aspheric lens with BBAR coating for the 3µm to 5µm wavelength range.