Detailed information about this product's features  T-Max passband tuner
This dual etalon Coronado SolarMax 90 is a brass and black 800mm focal length 90mm aperture f/8.9 refractor with a dual etalon Hydrogen-Alpha solar filter. The SolarMax 90 is in use around the world in private observatories and professional research facilities alike.
"Double-stacking" a Coronado solar filter uses two etalons in series to sharpen the filter’s normal <0.7 Ångstrom passband to a very narrow <0.5 Ångstrom centered on the 6562.8 Ångstrom H-Alpha line. This improves the filter’s contrast on subtle features in the active areas on the solar disk when compared to the <0.7 Ångstrom passband of the standard single etalon version (#SM90157), while only marginally reducing detail in the disk-edge prominences.
True double-stacking mounts a complete second 90mm etalon assembly in front of the SolarMax 90’s normal 90mm filter. This can be done either at the factory when the scope (our part number #SM9015DS) is manufactured, or a complete second 90mm filter assembly and adapter plate can be added at the factory at a later date (although at admittedly a much higher cost than buying the scope double-stacked to begin with).
In contrast, this dual etalon version uses the SolarMax 90’s normal full-aperture 90mm etalon in front of the objective lens, but has a factory-installed and performance-matched 60mm diameter second etalon mounted within the telescope barrel. The two etalons provide the increased contrast benefits of true double-stacking, but the smaller size (and consequently lower cost) of the 60mm internal etalon keeps the price of this dual etalon scope considerably below that of adding a complete second 90mm external etalon as is done with the #SM9015DS.
The scope’s custom-designed achromatic doublet lens uses special multi-layer antireflection coatings on all air-to-glass surfaces to optimize anti-ghosting and improve contrast. These vacuum-deposited hard coatings will provide a long lifetime of detailed solar observing. The scope delivers both diffraction-limited optical high resolution performance and the extremely high contrast needed to see both subtle surface details and the full explosive power of flares and prominences. With two and a quarter times better resolution than a 40mm solar scope (and 50% higher than a 60mm scope), and with over five times a 40mm’s light gathering ability (and two and a quarter times that of a 60mm scope) , the dual etalon SolarMax 90 can show you subtle details and contrast shadings that are simply invisible in any smaller solar scope.
The three-piece solar filter consists of a full-aperture 90mm etalon in front of the objective lens, a performance-matched 60mm diameter etalon mounted within the telescope barrel, and a 15mm clear aperture blocking filter in the scope’s 1.25" star diagonal. The result is a very narrow <0.5 Ångstrom passband for very high contrast in subtle prominence and disk features. The etalons are thermally stable, so there is essentially no drifting off the H-Alpha line as the filter heats up during use. (Thermal stability is 0.005Å per degree Centigrade.) The 15mm clear aperture of the blocking filter portion of the H-Alpha system in the star diagonal is matched in size to the focal length of the telescope to give you full disk views of the Sun.
The SolarMax 90 has two manual drawtubes that extend for rough focusing. One is located between the telescope body and the helical focusing ring around the drawtube. This 2" drawtube should be fully extended for visual work. The helical focuser provides the appropriate final fine focusing of the second manual 1.25" drawtube that projects through the helical focuser and can be extended as needed. This method provides enough back focus to allow both visual observing and afocal imaging. The 15mm blocking filter aperture allows you to use a Barlow in front of the SolarMax 90’s blocking filter/star diagonal. This makes digital photography easier and allows the use of a binoviewer with the SolarMax.
A T-Max passband tuner is installed between the solar filter etalon and the objective lens. This lets you mechanically tilt the filter’s passband off the H-Alpha line to observe Doppler-shifted solar activity. This will let you determine whether Doppler-shifted features, such as flares, are moving towards you or away from you as they leap off the surface of the Sun. For more details, click on the “T-Max" icon above.
A full set of 1.25" Coronado CEMAX eyepieces comes standard with the SolarMax 90. These eyepieces use proprietary anti-reflection multicoatings that have been optimized for the highest possible contrast during solar viewing of subtle prominence and surface detail. The set includes 25mm (32x), 18mm (44x), and 12mm (67x) CEMAX eyepieces. Also included, to double the magnification of the supplied CEMAX eyepieces, is the Coronado CEBAR 2x 1.25" Barlow. Like the CEMAX eyepieces, its performance and coatings are optimized for solar observing.
You can also use most 1.25" eyepieces in your collection with the Coronado SolarMax 90. Any good quality 50° field Plössl will work well, as a Plössl’s contrast is generally good and its field wide and flat. For optimum solar detail, however, the Coronado CEMAX eyepieces have a small, but visible, solar viewing contrast advantage over a conventional eyepiece designed for nighttime deep space observing.
A hard carrying case is standard equipment to transport and store the SolarMax 90. The scope comes with a clamshell tube mounting ring that allows you to mount the rather heavy (23 lb.) 30" long scope on most altazimuth and equatorial astronomical mounts. Also included is a Coronado Sol Ranger Sun Finder to make it easy to center the Sun’s image in the eyepiece. The Sol Ranger connects to the SolarMax 90’s clamshell mounting ring.
An alternative to this dual etalon scope is the Coronado #SM9015DS. This is a true double-stack model that adds a second factory-matched external 90mm etalon to the standard SolarMax 90 at the time your scope is built. The cost is considerably less than adding a second 90mm external etalon by returning your scope to the factory for retrofitting the second etalon at a later date.
This dual etalon scope, and the double-stacked version described above, are also available with a 30mm blocking filter built into a 2" straight-through eyepiece holder instead of the 15mm blocking filter/1.25" star diagonal combination. These versions let you mount 35mm format film and CCD imaging equipment in a straight-through configuration behind the 30mm blocking filter for full-disk solar images. The 30mm blocking filter version of this dual etalon scope is the #SM90305, while the true double-stack 30mm blocking filter version is the #SM9030DS. These versions are all provided with 2" to 1.25" adapter and a standard (no blocking filter) 1.25" star diagonal to let you use the supplied 1.25" CEMAX eyepieces for visual observing. The dual etalon SolarMax 90 cannot be used without having the external 90mm etalon attached to the scope.
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