This is a Plano-Concave Lens, type of Spherical Lens, offered by Standa. It is a Circular-shaped lens with a diameter of 25.4 mm and a base shape of Plano-Concave. The lens has a thickness edge of 3 mm and a thickness center of 2.6 mm, with an effective focal length (EFL) of -500 mm. The lens is made of CAF2 MAL-1963 material and is designed to operate at a wavelength of 2940 nm.
The lens does not have any coating, as indicated in the item data. The inner and outer radii are both 0, suggesting a simple, straightforward design. This lens is part of Standa's extensive catalog of optical elements, and the provided weblink indicates that it is currently in stock.