Much more than a simple minus-violet filter. Based on the popular Baader Moon&Skyglow filter, the Baader Contrast-Booster takes contrast enhancement and skyglow reduction to the maximum level possible from a filter. Not only does this filter deliver a significant enhancement of planetary and lunar contrasts, but it is designed to also totally eliminate the damaging blue defocused haze present in achromatic refractors. Gone are the annoying blue halo and obscuring haze that surround and smear resolution and contrast. Subtle contrasts and colors are boosted, while displaying the full resolution your scope is capable of.
The Contrast-Booster combines a special proprietary melt of Neodymium glass with a carefully designed 23 layer dielectric long-pass blocker on one face, and a 7-layer ultra-low antireflection coating on the other face. By aggressively filtering out the defocused blue wavelengths, a light yellow tint is imparted to objects (noticeably less than a typical yellow filter). The special coatings enable over 95% transmission across key portions of the visible spectrum (including H-Alpha). This results in a filter that retains the colors and color contrasts in tough subjects like Jupiter, without excessive image dimming. Cloud bands retain their ruddy red hues, but now become more striking in contrast. The Great Red Spot finally becomes easier. Planets and Lunarscapes are set against a jet black sky. The Contrast-Booster is a must for Solar observing (with Baader Astro Solar).
As many users have found, this is a great filter for Mars! The views of Mars with all telescopes (including reflectors and apochromats) benefit from the RGB filtration plus blue blocking.
Combined with the Baader UV-IR Cut filter, the Contrast-Booster makes the ideal filter set for digital imaging. Rather than add the cost of additional IR filtration (only needed for digital imaging), the Baader Contrast Booster has been optimized for visual use. Digital imagers can simply add the Baader UV-IR Cut filter when needed. The true 1/4 wave fineoptically polished surfaces guarantee the sharpness and contrast of the image.
Review from Astronomy Technology Today comparing the Baader fringe killer, semi-apo and contrast-booster filters.