Baader Planetarium 1.25″ Fringe Killer Filter
The Baader Planetarium Fringe Killer is a precision optical filter designed to minimize the unwanted blue fringing and haze that commonly affects achromatic refractors, while preserving natural color balance across the rest of the visible spectrum. Unlike stronger contrast filters that significantly alter color rendition, the Fringe Killer takes a more subtle approach - it selectively reduces transmission in the blue range between 450 and 480 nm, where most of the distracting false color originates, while maintaining approximately 95% transmission from that point through to 700 nm. The result is a noticeably cleaner image with natural-looking colors and no distracting purple or blue halo around bright objects.
Optical Construction
The filter's transmission curve is defined by nearly 100 individual coating layers applied to plane-parallel optical surfaces. This level of coating complexity is what allows the filter to achieve such a precise and well-defined cutoff in the blue range without degrading optical quality elsewhere in the spectrum. Images remain sharp, transmission losses are minimal, and the filter introduces no additional softening or scatter. For a 1.25″ filter in this price category, the optical specification is exceptional.
Practical Benefits for Achromatic Telescopes
Achromatic refractors are among the most popular telescope designs for beginners and casual observers, offering solid optical performance at an accessible price point. Their main limitation is residual chromatic aberration - a blue-violet fringe that appears around high-contrast objects such as the Moon, bright planets, and stars against a dark background. The Fringe Killer effectively suppresses this artifact and allows the telescope to perform closer to its true optical potential.
Comparable performance in terms of chromatic aberration correction can only be achieved with apochromatic refractors, which typically cost 20 times more or even higher. The Baader Fringe Killer offers a practical and affordable alternative that extracts the best possible image quality from a standard achromatic instrument.
Filter Combinations
The Fringe Killer also works exceptionally well in combination with other filters. Paired with a Baader 610 nm red filter, it forms a 70 nm wide H-alpha filter with a very high transmission of 95% - making it one of the most cost-effective ways to observe and photograph H-alpha emission structures. Combined with the Baader Neodymium Moon and Skyglow filter, it produces outstanding contrast on lunar and planetary detail, revealing surface structures with a clarity that is difficult to achieve with either filter alone.
Technical Specifications
- Filter size: 1.25″ (fits standard 1.25″ eyepiece barrels)
- Transmission range: restricted between 450-480 nm (blue), approximately 95% from 480 nm to 700 nm
- Optical surfaces: plane-parallel with nearly 100 coating layers
- Color rendition: color-balanced - no significant color shift
- Primary application: achromatic refractors, Moon, planets
- Housing: precision-threaded metal cell
