Baader Energy Rejection Filter (D-ERF) - H-Alpha Solar Observation Filter

The Baader Energy Rejection Filter (D-ERF) is specifically designed for H-alpha solar observation, allowing telescopes to achieve full-aperture resolving power. This filter significantly reduces the thermal energy entering the telescope, protecting your solar spectrum filter and minimizing thermally-induced seeing effects for a more stable and detailed observation experience.

Advanced Coating Technology

Each Baader D-ERF filter is crafted with precision using the world's most advanced optical coating technology. The filter layers are applied with a 43-layer dielectric DWDM-coating, ensuring only a “cool” 45nm-wide red light beam around the H-alpha wavelength reaches the solar filter system. Every filter undergoes rigorous quality checks on a Carl Zeiss optical bench in Germany, ensuring unmatched performance and durability.

Optimized for Heat and Scratch Resistance

The D-ERF filter is made from clear BK7 glass, polished to match objective-lens standards. With all reflection coatings applied to one side, it effectively blocks unwanted wavelengths from 280nm to 1500nm while maintaining a 45nm spectral window around the H-alpha wavelength. This high-quality design keeps heat load low and ensures scratch resistance, extending the filter’s life and reliability for solar observation.

Specifications

• Transmission Range: 610 – 690 nm
• Filter Thickness (without cell): 12.5 mm
• HBW (Halfbandwidth): 80 nm
• CWL (Central Wavelength): 650 nm
• AR-Coating: Dielectrically coated, planeoptically polished
• Filter Usage: IR-Cut, Solar, Specialty, UV-Cut
• Filter Shape: Round
• Filter Size Options: 75mm, 90mm, 110mm, 135mm, 160mm, 180mm

Available Sizes

The Baader D-ERF filters are available in multiple sizes to fit various telescopes:

• 75mm: Ø 75 mm ± 0.05 mm
• 90mm: Ø 89.9 mm ± 0.05 mm
• 110mm: Ø 109.9 mm ± 0.05 mm
• 135mm: Ø 134.9 mm ± 0.05 mm
• 160mm: Ø 159.9 mm ± 0.05 mm
• 180mm: Ø 179.9 mm ± 0.05 mm

Why Choose the Baader D-ERF Filter?

The Baader D-ERF filter is the ultimate choice for serious solar astronomers. It not only enhances solar image quality by reducing heat-induced distortions but also protects delicate H-alpha filters from excessive thermal energy. With its scratch-resistant coating and durability, this filter is built to last, offering reliable performance across a variety of telescope setups.