OptoSigma's FNDU-20C02-40 is a 20 mm diameter, unmounted reflective neutral density filter, designed for use in the ultraviolet range of 200-400nm. This filter is part of the UVFS series, identified by the material ID "uvfs mal- 1965".
The filter features a thickness of 2mm, providing a balance between durability and minimal impact on the optical path. It boasts a base shape of a circle, a common choice for versatility and ease of integration into various optical systems.
The coating on both the front and back surfaces of the filter is "opt fndu-40". This coating is specifically designed for neutral density filters, ensuring consistent attenuation across the spectral range without introducing unwanted color casts.
The filter's geometry, including its diameter and thickness, classifies it as a thin lens. This designation suggests that the filter has a minimal effect on the overall optical system, making it an ideal choice for applications where maintaining the original optical path is crucial.