The Lunt LS60TDS2 double stack 60mm solar refractor is designed for serious high resolution Hydrogen-alpha solar viewing. The H-alpha views through the Lunt 60mm solar refractor show you much more of the living Sun than ordinary glass or Mylar white light solar filters that show only sunspots. With the Lunt LS60TDS2, you see the violent ever-changing tapestry of multiple prominences leaping off the edges of the solar disk and the explosive upheavals of flares and filaments on the face of the Sun. All of this is visible in addition to sunspots and surface features in exquisite detail.
In addition, the best and most-detailed H-alpha views of the Sun are undoubtedly seen thru a dual etalon (double stacked) scope like this Lunt 60mm. The reduction in passband from a single etalon’s 0.8 Ångstroms to under 0.55 Ångstroms with the double stack seems to bring the Sun's surface to life with a palpable Wow! reaction from virtually all who experience a double stack Sun. However, adding a second etalon to an existing etalon is not quite as simple as it may seem. Both etalons need to be brought on line (tuned) and both need to be tiltable such that all ghosts are eliminated when viewing or imaging. Ideally the transmission curves should overlap perfectly when on band to provide for the best possible resolution and contrast.
The Lunt LS60TDS2 consists of a 500mm focal length 60mm aperture f/8.33 refractor with an integrated double stack Hydrogen-alpha solar filter. The factory-matched tunable external/internal double etalon system allows use at both a wider <0.8 Ångstroms passband working at f/8.33 for brighter prominences and a narrower <0.55 Ångstroms passband working at f/10 for higher contrast views of surface features.
The three-part filter uses a single pass 60mm internal etalon, a single pass 50mm external etalon, and a 12mm blocking filter built into the standard equipment 1.25” star diagonal. There is also an infrared reflecting window (Energy Reflecting Filter or ERF) early in the optical path to remove unwanted heat from the system. Both etalons in the system are matched at the factory to provide a system optimized for maximum performance and the elimination of ghosting. A tilt-tuning mechanism built into the system lets you center the passband precisely on the H-alpha line for maximum contrast, as well as perform off-band observations of Doppler-shifted disk features to determine whether they are moving towards you or away from you.
The scope’s singlet objective lens is fully multicoated. It is not necessary to use an achromatic doublet in a small solar scope to correct for chromatic aberration in the violet end of the visible spectrum. Solar scopes are designed to observe only a single wavelength of red light at the opposite end of the spectrum. Why pay for two lenses to cure a problem that a solar scope is incapable of showing you in the first place? In addition, the front singlet lens design reduces the stray light of a two-lens achromat’s internal reflections by half. With the matched collimation lens set built into the scope, it also fully corrects for on-axis coma, astigmatism, and de-centering aberrations and provides a spherically corrected flat-field image.
If the scope is used without the removable external etalon, the system has a <0.8 Ångstrom passband, centered on the 6562.8 Ångstrom H-alpha line. The sub-Ångstrom passband width gives you balanced views of feathery prominences and low-contrast surface detail alike. If the external etalon is added to the scope, the passband narrows to <0.55 Ångstroms for substantially higher contrast surface details, although with a slight loss of prominence brightness. The filter is thermally stable, so there is no drifting off the H-alpha line as the filter heats up during use. The 12mm clear aperture of the blocking filter portion of the H-alpha system (which is built into the star diagonal housing) is ideally matched to the focal length of the telescope to give you an approximately 4.5mm diameter image of the full disk of the Sun at prime focus. This 12mm B1200 blocking filter is better suited for binoviewer use, and for imagers who need a wider illuminated field for use with cameras having a long back focus, than the primarily visual and lower-priced 6mm blocking filter version (#LS60TDS).
Coarse focus is via a sliding drawtube. Fine focus is achieved using the standard equipment dual-speed Crayford focuser that has a 10:1 reduction ratio for precision focusing on the smallest of solar details. Large ribbed focusing knobs make it easy for you to reach a precise focus, even if you are observing in the dead of winter while wearing gloves or mittens.
You can use virtually any 1.25” eyepiece with the 60mm Lunt solar refractor. A typical 20mm 1.25” Plössl will give you a magnification of 25x and a little over a 2° field of view compared with the 0.5° diameter disk of the Sun. A 15mm Plössl will give you 33.3x and about a 1.5° field, giving you plenty of dark sky background around the solar disk to show off the prominences.
The Lunt LS60TDS2 comes with a clamshell-type mounting ring with 1/4”-20 thread holes that will let you mount the scope directly on a photo tripod for a quick peek at the Sun. You can also mount the clamshell ring on a dovetail plate and install it on an altazimuth or equatorial mount for extended observing and tracking of the Sun. A foam-lined hard case is standard equipment for transporting and storing your Lunt scope.