Lunt LS40F Hydrogen-Alpha Front-Mounted Etalon System

To measure for your adapter plate take a measurement of the outside diameter of the dew shield on your refractor telescope. If measuring in inches, multiply the measurement by 25.4 to find your measurement in millimeters.

The LS40F brings hydrogen-alpha solar observing within reach. This 40mm front-mounted etalon converts your existing refractor into a capable solar telescope, revealing prominences, filaments, active regions, and chromospheric detail at a price point that makes H-alpha accessible.

The LS40F uses a center-supported etalon design—an approach with proven heritage in solar filtration—paired with precision tilt tuning for smooth wavelength control. The design delivers a <0.65 angstrom bandpass: tight enough for rewarding views of solar activity, and an excellent foundation for observers ready to explore the chromosphere.

Each system ships complete with a B600 blocking filter (6mm clear aperture, for focal lengths up to 540mm) and a custom adapter plate machined to fit your telescope. Provide your objective cell diameter when ordering, and we'll include the correct adapter at no charge—accommodating refractors with objective housings up to 4 inches.

Remove the system in seconds to return your refractor to nighttime duty.

Technical Note: This system is designed with a center-mounted foot to support the etalon. Consequently, the filter is center-obstructed.   

Specifications:

• 40mm etalon with center-supported design (Note: Filter is center-obstructed)
• <0.65 angstrom bandpass (H-alpha, 656.28nm)
• Tilt-tuned wavelength control
• B600 blocking filter included (6mm CA, up to 540mm FL)
• Custom adapter plate included (up to 4" objective cells—specify diameter at checkout)
• Visual and imaging capable