The Baader Semi-APO filter is one of the most advanced 'minus-violet' type filters available.
Remarkably efficient and neutral, it practically disappears in use while removing most of the violet fringe! The effects are remarkable, even with small refractors.
The RGB enhancement of the Neodymium substrate also makes this a superb planetary filter, particularly for Jupiter and Mars.
This filter is best suited to semi-apo or long focal-length achromat refractor telescopes.
Used, in perfect condition.