William Optics SDC Astro Filter

The multispectra design selectively blocks common sources of light pollution while allowing specific wavelengths emitted by deep-sky objects to pass through. This increases the contrast between your target and the background sky, making faint details in nebulae and galaxies much easier to pull out during processing.

This is a standard 2-inch round filter, which is compatible with most 2-inch focusers, filter wheels, and diagonal adapters. As long as your imaging train accepts standard 2-inch threaded filters, it should fit without issue.

While it is optimized for astrophotography, you can certainly use it for visual observation. It will help darken the background sky and improve the contrast of emission nebulae, though the view may appear slightly dimmer due to the light-blocking nature of the filter.

The SDC Ultra Layer coating is designed to minimize internal reflections and ghosting, which are common issues when shooting bright stars. By reducing these optical artifacts, the coating helps maintain sharp, clean images even when capturing high-contrast subjects.

Yes, adding any filter to your imaging train shifts the focal plane slightly. Because this glass is 2mm thick, you should account for a small shift in back-focus—typically about one-third of the filter's thickness—when calculating your spacing to ensure your images remain perfectly sharp.