Lacroix Optical part #16548. Square plano concave lens 30mm square by -269.42mm focal length. 10mm thick. Because of the thickness this was probably made for high power laser applications. Glass is S-4003 (very dark glass and doesn't appear to pass visible light)) and has very high precision surface spec of 10-5 scratch/dig. Spec sheet will be included with your order. Unused. Only have a few.
