This is the LF1988-B 25.4 mm Dia. N-BK7 Negative Meniscus Lens, a high-quality optical component sourced from Thorlabs. This lens is designed for use in the 650-1050nm wavelength range, making it suitable for a wide range of optical applications.
The lens is spherical in shape, with a base shape of a circle. It has a diameter of 25.4 mm and a thickness at the edge of 3.3 mm, while the center thickness is 3 mm. The effective focal length (EFL) of this lens is -500mm, indicating that it is a negative or concave lens. The first radius of curvature (R1) is 250 mm, and the second radius of curvature (R2) is 126.3 mm. The back focal length (BFL) is -496.3 mm.
The lens is made from N-BK7 Schott glass, a popular material for optical elements due to its excellent optical properties. The lens is coated with THo BBAR on both the front and back surfaces to enhance its performance in the specified wavelength range.
The web link provided leads to the product page on Thorlabs' website, where you can find more information about this lens, including its availability and pricing.