The Baader Semi APO Filter 1.25" delivers an amazingly neutral view, while cutting most of the annoying and contrast-robbing violet fringe that plagues all achromats. The Semi-APO filter combines a stronger Fringe Killer coating formula with the Moon & Skyglow Neodymium substrate. The result is similar performance to the Fringe Killer + Moon&Skyglow combination, but with a slightly stronger violet cut. It's high efficiency and neutral coloration make it practically disappear in use - while making most of the violet fringe disappear! The effects on sharpness, contrast and aesthetics are remarkable, even with small refractors. The RGB enhancement of the Neodymium substrate actually boosts color contrasts, particularly for Jupiter and Mars.