Lunt blocking filter for H-alpha sun observation B400 - angled return 1.25″

Lunt B400 blocking filter: Solar observation in H-alpha light

The Lunt B400 blocking filter, integrated into a 1.25" angled return, is an essential component for observing the Sun in H-alpha light. Designed to guarantee total safety and exceptional image quality, this filter is specifically optimized to isolate the Hydrogen Alpha spectral line (656.28 nm), enabling the fascinating details of the solar chromosphere, such as protuberances, filaments and active regions, to be revealed. Compact and reliable, it is ideal for short-focus solar telescopes such as the LS50THa, and is aimed at solar astronomy enthusiasts wishing to explore the Sun in complete safety.

What is the purpose of a blocking filter?

Unlike a front filter or Fabry-Perot etalon, the blocking filter plays a crucial role in the optical system of an H-alpha solar telescope. Whereas the etalon isolates a narrow band around the H-alpha line, the blocking filter acts as a "spectral cleaner", eliminating all unwanted harmonics and stray wavelengths. This ensures that only light centered on 656.28 nm reaches the eyepiece or camera.

The B400 blocking filter incorporates several filter layers:

• Blue filter : Dims brightness and blocks infrared (IR).
• Red UV filter : Absorbs harmful ultraviolet rays.
• Band-pass filter : Reflects only H-alpha light towards the eyepiece.
• Final filter : Blocks all residual wavelengths.

This multi-layer system ensures sharp, high-contrast, eye-safe viewing.

Key features

• Blocking filter diameter : 4 mm (B400), optimized for short focal lengths up to 400 mm.
• Integrated angled return : 1.25" format, compatible with a wide range of standard eyepieces.
• Maximum safety : Complies with international standards for safe solar observation.
• Spectral optimization : Eliminates unwanted harmonics to isolate exclusively the H-alpha line (656.28 nm).
• Robust construction: Made of machined aluminum with high-precision optical components.

Why choose the Lunt B400 blocking filter?

• Optimized visual observation : The B400 is specially designed to offer a field of view suitable for visual observation of the complete solar disk with short-focus telescopes.
• Outstanding image quality : Thanks to its multi-layer system, it guarantees sharp, high-contrast images without light interference.
• Absolute safety : Effectively blocks harmful UV and IR radiation, ensuring safe use for your eyes.
• Universal compatibility : Works with all Lunt solar telescopes equipped with a 1.25" angled return.
• Compact and portable: Ideal for use on the move or with compact telescopes such as the LS50THa.

Recommended applications

• Visual observation of the Sun in H-alpha : Explore solar protuberances, filaments and active regions with optimal contrast.
• Light astrophotography : Compatible with cameras equipped with small sensors.
• Ideal for short focal lengths (up to 400 mm) on compact instruments.