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Meade - ETX-90 Spotting Scope with UHTC Coatings with 3 Year Sky Assurance
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$ 434.99
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| 3514-00-02SP_SKY
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For high-resolution imaging of terrestrial subjects, Meade ETX Spotting Scopes are two of the
finest instruments ever developed at any price. Explore the subtleties of a bird’s feather
structure at 50 yards; read license plates more than half a mile in the distance; observe people
walking on a street two miles in the distance; or use an ETX Spotting Scope for casual
astronomical observations of the Moon, planets, and deep-space. The possibilities are as
limitless as your own imagination.
Meade ETX Spotting Scopes include the exact same astronomical-quality, diffraction-limited
optical tube assemblies as their respective Astro Telescope versions. As a result these systems
far outperform other terrestrial telescopes not manufactured to within such precise optical
tolerances. ETX Spotting Scopes do not, however, include the Astro Telescopes’ fork mountings or
internal motor drives, features specifically designed for extensive astronomical applications.
Flip-mirror systems on each unit permit quick adaptation from visual observing at 90°, to
fully-image-erect viewing at 45°, to through-the-telescope 35mm photography with the optional #64
T-Adapter. Armed with their extremely long focal lengths (1250mm for the ETX-90), and yet mounted
in relatively short, portable tube assemblies, ETX optics reveal distant photographic detail far
beyond the capabilities of standard focal length lenses and without the physical inconvenience of
typical long lenses.
The ETX-90 Spotting Scope is an ideal terrestrial instrument in virtually any observing
environment; the majority of first-time users are startled by the level of visible detail and
resolution. In situations where the subject is at a greater distance from the observer, or where
lighting conditions are less than perfect,
Specifications:
* Includes Maksutov-Cassegrain optical tube assembly (ETX-90: D = 90mm, F = 1250mm, f/13.8;
* With MgF2 coatings on the correcting lens and standard aluminum coatings on the primary and
secondary mirrors (Ultra-High Tranmission Coatings, available optionally);
* Internal flip-mirror system for either straight-through or 90° observing position;
* 8 x 21mm achromatic erect-image viewfinder ;
* Series 4000 Super Plössl 26mm eyepiece for 48X ;
* #932 45° Erecting Prism; tripod adapter block for attachment of the spotting scope to any
standard (1/4-20) photo tripod;
* Operating instructions.
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An important optional feature to optimize the performance of your Meade
telescope.
Image brightness in a telescope is crucially dependent on the reflectivity of
the telescope’s mirrors and on the transmission of its lenses. Neither of
these processes, mirror-reflectivity or lens-transmission, is, however,
perfect; light loss occurs in each instance where light is reflected or
transmitted. Uncoated glass, for example, reflects about 4% of the light
impacting it; in the case of an uncoated lens 4% of the light is lost at
entrance to and at exit from the lens, for a total light loss of about 8%. |
Early reflecting telescopes of the 1700’s and 1800’s suffered greatly from mirrors of poor
reflectivity- reflection losses of 50% or more were not uncommon. Later, silvered mirrors
improved reflectivity, but at high cost and with poor durability. Modern optical coatings have
succeeded in reducing mirror-reflection and lens-transmission losses to acceptable levels at
reasonable cost.
Meade Standard Coatings: The optical surfaces of all Meade telescopes include high-grade optical
coatings fully consistent in quality with the precision of the optical surfaces themselves. These
standard-equipment coatings include mirror surfaces of highly purified aluminum, vacuum-deposited
at high temperature and overcoated with silicon monoxide (SiO), and correcting lenses coated on
both sides for high light transmission with magnesium fluoride (MgF2). Meade standard mirror and
lens coatings equal or exceed the reflectivity and transmission, respectively, of virtually any
optical coatings currently offered in the commercial telescope industry.
The Meade UHTC Group: Technologies recently developed at the Meade Irvine coatings facility,
however, including installation of some of the largest and most advanced vacuum coating
instrumentation currently available, have permitted the vacuum-deposition of a series of exotic
optical coatings precisely tuned to optimize the visual, photographic, and CCD imaging
performance of Meade telescopes. These specialized, and extremely advantageous, coatings are
offered here as the Meade Ultra-High Transmission Coatings (UHTC) group, a coatings group
available optionally on many Meade telescope models.
In Meade catadioptric, or mirror-lens, telescopes (including the ETX-90EC, ETX-105EC and
ETX-125EC; LX10, LX90, and LX200GPS Schmidt-Cassegrains; and LXD55-Series Schmidt-Newtonians)
before incoming light is brought to a focus, it passes through, or is reflected by, four optical
surfaces: the front surface of the correcting lens, the rear surface of the correcting lens, the
primary mirror, and the secondary mirror. Each of these four surfaces results in some loss of
light, with the level of loss being dependent on the chemistry of each surface’s optical coatings
and on the wavelength of light. (Standard aluminum mirror coatings, for example, typically have
their highest reflectivity in the yellow region of the visual spectrum, at a wavelength of about
580nm.)
Mirror Coatings: Meade ETX, Schmidt-Cassegrain, and Schmidt-Newtonian telescopes equipped with
the Ultra-High Transmission Coatings group include primary and secondary mirrors coated with
aluminum enhanced with a complex stack of multi-layer coatings of titanium dioxide (TiO2) and
silicon dioxide (SiO2). The thickness of each coating layer precisely controlled to within +/-1%
of optimal thickness. The result is a dramatic increase in mirror reflectivity across the entire
visible spectrum; at the important hydrogen-alpha wavelength of 656nm. - the predominant
wavelength of emission nebulae - reflectivity is increased from 89% to over 97%.
Correcting Lens Coatings: Meade telescopes ordered with the UHTC group include, in addition, an
exotic and tightly-controlled series of coatings on both sides of the correcting lens or
correcting plate, coatings which include multiple layers of aluminum oxide (Al2O3), titanium
dioxide (TiO2), and magnesium fluoride (MgF2). Per-surface light transmission of the correcting
lens is thereby increased at the yellow wavelength of 580nm., for example, to 99.8%, versus a
per-surface transmission of 98.7% for the standard coating.
The importance of the UHTC group becomes apparent when comparing total telescope light
transmission, or throughput, caused by the multiplier, or compounding, effect of the four optical
surfaces. With each optical surface contributing significantly to telescope light throughput, the
effect of all four surfaces combined is indeed dramatic, as demonstrated by the graphs on the
facing page, as well as by the table of the brightest nebular emission lines. At the H-alpha
wavelength of 656nm., total transmission increases from 77% to 93%, an increase of 93/77 or 21%
at all three nitrogen-III and sulfur-II wavelengths of 655nm. and 673nm.- prominent lines in
certain galactic nuclei and in supernova remnanats such as the Crab Nebula- transmission
increases by 21%; ; at the helium wavelengths of 588nm. and 469nm. - strong emission lines in hot
planetary nebulae - total telescope transmission increases by 18% and 19%, respectively; at the
two nitrogen II lines of 655nm. and 658nm. and at the sulfur II line of 673nm., transmission is
increased by 21%. Averaged over the entire visible spectrum (450nm. to 700nm.), total light
transmission to the telescope focus increases by about 20%.
Observing with the UHTC: Meade ETX, Schmidt-Cassegrain, and Schmidt-Newtonian telescopes equipped
with the UHTC present dramatically enhanced detail on the full range of celestial objects - from
emission and planetary nebulae such as M8, M20, and M57 to star clusters and galaxies such as M3,
M13, and M101. Observations of the Moon and planets, since they are observed in reflected (white)
sunlight, benefit in image brightness from the full spectrum of increased transmission. The
overall effect of the UHTC is, as it relates to image brightness, to increase the telescope’s
effective aperture. Image brightness (i.e., the ability to see faint detail) of the Meade 10”
LX200GPS is, for example, effectively increased by about one full inch of aperture.
| Emission Line | Wavelength (nm.) | Transmission: Standard Coatings
(%) | Transmission: UHTC Group (%) | Increase* |
| Hydrogen-alpha (Ha) | 656 | 76.9 | 93.1 | 21% |
| Hydrogen-beta (Hß) | 486 | 75.3 | 85.8 | 14% |
| Oxygen III | 496 | 76.5 | 85.4 | 12% |
| Oxygen III | 501 | 77 | 85.4 | 11% |
| Helium II | 496 | 72.5 | 86.1 | 19% |
| Helium I | 588 | 79.5 | 93.5 | 18% |
| Nitrogen II | 655 | 77 | 93.2 | 21% |
| Nitrogen II | 658 | 76.7 | 92.8 | 21% |
| Sulfer II | 673 | 75.7 | 91.8 | 21% |
* The % increase is obtained by dividing the UHTC-transmission (column 4) by the
standard coatings transmission (column 3).
Effects on CCD Imaging: While the human eye loses sensitivity to light beyond wavelengths of
about 700nm., CCD imaging chips remain sensitive to about 750nm. and longer, wavelengths at which
the reflectivity of an aluminum coating is near its lowpoint. Importantly, however, the UHTC’s
total light transmission at 750nm. is 83%, vs. 72% for standard coatings, an increase of 83/72,
or 15%.
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