Lumicon 1.25" Minus Violet Filter – Reduces Chromatic AberrationThe Lumicon 1. 25" Minus Violet Filter blocks violet and ultraviolet light shorter than approximately 420nm to help bracket the color corrected band of refracting telescopes. It reduces blue halos around bright objects and minimizes chromatic aberration in photographs. It is also useful as a visible light filter in RGB astrophotography with reflecting telescopes. Key Features Cuts off wavelengths below ~420nm Reduces purple fringing and blue halos