Lunt LS40FHa Front Mount 40mm Double Stack Solar Filter

LS40FHa — 40mm Front-Mount Double Stack Solar Filter The double-stack upgrade for the Lunt LS40THa series. Two 0.35Å etalons in series — the tightest combined bandpass in the Lunt range.

Now with new-generation etalons — every unit individually tested on Lunt's precision metrology equipment. Every specification is verified, not estimated.

The LS40FHa is a 40mm aperture front-mounted tilt-tuned etalon designed for two purposes — as a double-stack upgrade for the Lunt LS40THa dedicated 40mm solar telescope series, or as a standalone H-alpha solar filter for a compatible customer-supplied refractor.

As a double-stack filter for the LS40THa: The LS40FHa adds a second 0.35Å etalon to the optical path, placing two etalons of equal specification in series with the LS40THa's own front-mounted etalon — delivering a combined system bandpass of <0.25Å. This is the tightest combined bandpass available in any Lunt double-stack configuration. Because both etalons are front-mounted tilt-tuned at 0.35Å — rather than pairing a front-mount filter with an internal pressure-tuned etalon — the in-series result is tighter than larger double-stack systems. At <0.25Å, chromospheric detail that single-stack instruments at this aperture cannot resolve becomes visible: plage boundaries sharpen into cellular networks, filaments reveal dark cores and multi-strand structure, and prominences show internal threading from base to tip.

As a standalone H-alpha filter for customer refractors: The LS40FHa can be used on a compatible customer-supplied refractor as a standalone front-mounted H-alpha filter. A Lunt blocking filter must be used at all times — this is a safety requirement. If you are looking for a complete standalone package including a blocking filter and adapter, Lunt offers complete front-mounted filter packages that include both.

Installation requires no tools and no factory visit. A Lunt blocking filter is required for safe operation — the LS40FHa is not a standalone safety device.

Specifications

• Model: LS40FHa
• Optical Aperture: 40mm — no central obstruction
• Tuning: Tilt-tuned
• Single Etalon Bandpass: 0.35Å — individually verified
• Combined System Bandpass: <0.25Å — two 0.35Å tilt-tuned etalons in series
• Compatible With: LS40THa series (DS); compatible customer refractors (standalone)
• Focal Length: 400mm (unchanged)
• Blocking Filter Required: Yes — sold separately (B500 or B600 recommended)
• Weight: ~1 lb (~0.4kg)
• Storage: Aluminum hard case with fitted foam (optional)