Detailed information about this product's features  T-Max passband tuner
This true “double-stack" Coronado SolarMax 90 consists of a brass and black 800mm focal length 90mm aperture f/8.9 refractor with two full aperture 90mm Hydrogen-Alpha solar filter etalons in series in front of the objective lens. The SolarMax 90 is the largest Hydrogen-Alpha solar telescope ever to be mass-produced and is in use around the world in private observatories and professional research facilities alike.
Double-stacking the filters sharpens a single filter’s normal <0.7 Ångstrom passband to a very narrow <0.5 Ångstrom centered on the 6562.8 Ångstrom H-Alpha line. This visibly 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.
In addition, this scope’s true double-stacked filter mounts the second 90mm full aperture etalon assembly directly in front of the SolarMax 90’s normal 90mm etalon, with both installed in front of the objective lens. This is optically more effective than the dual etalon method (#SM90155) that places a smaller diameter etalon part way down the telescope tube, behind the objective lens. With the true double-stacking method used here, light rays remain parallel while passing through the two 90mm filters. With the dual etalon method, the light rays are converging as they reach the second etalon (having passed through the achromatic doublet lens at the front of the scope). This affects the spread of the internal reflections within the second etalon, reducing the sharpness of the filter cut-off and the shape of the passband.
The cost of this factory-matched double-stack scope is somewhat less than the cost of adding a complete 90mm filter assembly to a single filter SolarMax 90 yourself at a later date, as can be done. Aside from the slightly lower cost, however, this double-stack scope package pairs factory-matched full aperture etalons, which typically perform better than simply adding an unmatched second etalon yourself in the field at a later date.
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 two full-aperture 90mm etalons in front of the objective lens 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 views of 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 (25 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.
A less expensive alternative to this double-stack scope is the Coronado #SM90155. This is a dual etalon model that adds a second factory-matched internal 60mm etalon to the standard SolarMax 90, rather than a second 90mm external etalon. The cost is considerably less than this double-stack version, but with almost the same level of performance. With either version, double-stack or dual etalon, the factory matching of the etalons provides higher performance than simply adding an unmatched second etalon yourself later.
This double-stacked scope, and the dual etalon 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 double-stack scope is the #SM9030DS, while the 30mm blocking filter dual etalon version is the#SM90305. 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.
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