This is a 13-153 12.5 mm Dia. Hoya Neutral Density (ND) Filter, specifically designed for use in the Near-Infrared (NIR) spectrum with a wavelength of 900nm. The filter is manufactured by Edmund Optics, a leading supplier of optical components.
The filter is of the absorptive type, meaning it reduces the intensity of light by absorbing it rather than reflecting or scattering it. This is achieved through the use of a special coating, denoted as 'edm 13-153' on both the front and back surfaces of the filter. This coating is designed to provide a Neutral Density of 0.7 (ND-25), which means it reduces the light intensity uniformly across the entire spectrum, without altering the color balance.
The filter has a circular shape with a diameter of 12.5mm and a thickness of 3.1mm, making it suitable for use in a variety of optical systems. The geometry of the filter is designed to mimic a thin lens, which can help to minimize optical aberrations and distortions.
The filter is currently in stock and available for purchase directly from the Edmund Optics website, with the catalog number 13-153. The link to the product page is provided in the item data for your convenience.