Lunt LS80MT Modular Solar Telescope - Pressure Tuned

Optical Design and Nighttime Performance

At its core, the LS80MT uses an 80 mm FPL-53 ED doublet objective with a focal length of 560 mm at f/7. This optical configuration delivers excellent color correction, high contrast, and sharp star images when used as a nighttime refractor. In its non-solar configuration, the telescope functions as a true apochromatic refractor suitable for lunar, planetary, and deep-sky observing and imaging. The optical quality and focal ratio also make it well suited for modern astrophotography workflows when paired with appropriate accessories.

Hydrogen-Alpha Etalon System

For solar observation, the LS80MT integrates an internal Fabry-Pérot hydrogen-alpha etalon with a typical bandpass of less than 0.65 angstrom. This narrow spectral window isolates the hydrogen-alpha wavelength at 656.28 nm, revealing fine chromospheric structures such as filaments, prominences, plages, and active regions. The internal placement of the etalon protects it from environmental exposure and contributes to long-term stability and consistent optical performance under varying thermal conditions.

True Doppler Pressure Tuning Technology

The LS80MT employs Lunt’s Internal Pressure Tuning system, a defining feature that provides significant advantages over mechanically tilt-tuned designs. By adjusting the internal air pressure within a sealed etalon chamber, the refractive index of the air is altered, shifting the etalon precisely onto the hydrogen-alpha wavelength. This barometric tuning method produces uniform contrast across the entire solar disk and minimizes field-dependent sweet spots. In addition, pressure tuning allows true Doppler shifting, enabling the observer to tune slightly on and off band to explore velocity-dependent solar phenomena. This capability is essential for studying the three-dimensional structure of filaments and the high-velocity dynamics of prominences and eruptive events along the solar limb.

Blocking Filter Options and Image Circle

A critical component of the LS80MT system is the blocking filter, which determines the size of the illuminated image circle and the suitability for different applications.

• B1200 (12mm):This filter is the standard choice for visual observers. It provides a generous field of view that comfortably frames the entire solar disk, offering crisp views through most medium-to-high power eyepieces.
• B1800 (12mm):For the dedicated astrophotographer or those using larger-format sensors, the B1800 is the recommended upgrade. The larger aperture prevents vignetting on modern CMOS sensors and provides a wider, fully illuminated field. This extra "breathing room" is also beneficial for those using binoviewers or high-magnification Barlow lenses, ensuring that the solar limb remains fully bright and detailed across the entire frame.

Modular Architecture and Multi-Wavelength Capability

As part of Lunt’s MT series, the LS80MT is defined by its modular architecture. In its standard configuration, it operates as a dedicated hydrogen-alpha solar telescope. The entire H-alpha module can be removed, converting the instrument into a conventional 80 mm ED apochromatic refractor in minutes. This design allows seamless transition between solar observation and nighttime astronomy without permanent modification. The system is also compatible with Lunt Calcium-K modules and white-light Herschel wedges, providing a flexible and future-proof platform for multi-wavelength solar research.

Mechanical Design and Build Quality

The LS80MT is constructed to the same standards as Lunt’s larger observatory instruments. It features a heavy-duty dual-speed rack-and-pinion focuser with a 10:1 fine-focus reduction, allowing precise focusing at high magnifications and during critical imaging. The optical tube is installed in CNC-machined mounting rings and a dedicated solar finder handle for safe and efficient alignment. The telescope is supplied in a custom-fitted, aluminum finished hard case, ensuring long-term protection and reliability under the demanding thermal conditions associated with solar observation.