CXB (formerly Astrodon) 5nm Narrowband SII Filter (Sulfur II) FarSight These two factors combine to

These two factors combine to provide you with the highest contrast available

because a longer tube costs money to ship

25″ (pre-2008) — Armored

25 Inch #47 Violet Color Filter can be used when looking for polar caps on Mars

That matters when back-focus is critical \u2014 some telescopes and accessory combinations simply can\u2019t reach focus with a full-length adapter in the path

CXB (formerly Astrodon) 5nm Narrowband SII Filter (Sulfur II) FarSight These two factors combine toNotice: As of 9 23 2025 New production has been started. We have had some filter yeild from the intial testing runs and those filter are available for purchase now. Please monitor our website for upcoming notices of availability dates and the ability to place pre orders. Status of the filter sizes are as follows: SII 5nm 1. 25" mounted release date TBD (check back soon) SII 5nm 36mm round unmounted release date TBD (check back soon) SII 5nm 50mm round