This is the FND-15C02-40, a 15 mm diameter unmounted Neutral Density Filter from OptoSigma. The filter is made of N-BK7, a high-quality glass material from Schott, ensuring excellent optical performance. It is designed for use in the visible spectrum, specifically between 400 and 700 nanometers.
The filter features a reflective neutral density coating on both the front and back surfaces, denoted as 'opt fnd-40'. This coating reduces the intensity of light passing through the filter without altering its color, making it ideal for applications where light intensity needs to be controlled, such as in photography or scientific research.
The filter has a thickness of 2 millimeters and a circular shape, following a thin lens geometry. This makes it compatible with various optical systems and setups. The 'FND-15C02-40' is currently in stock and available for purchase through the OptoSigma website.