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As you already know, the LX90 is the ultimate all-around telescope for the money. Now, with the addition of Advanced Coma Free
optics, Meade has taken the LX90 to an even higher level above the competition. Meade have raised the bar both for visual viewing
and astrophotography without raising the price. The LX90-ACF optical system delivers wide, coma-free images with pinpoint stars
all the way out to the edge of the field. Now the amateur can have this amazing RC like performance for the price of an ordinary
SC. All LX90-ACF Advanced Coma-Free Telescopes include a Sony GPS Receiver, 8x50 Optical Viewfinder, Smart Finder (Red Dot Finder),
Patented Level North Alignment Technology (LNT), AutoAlign, Oversized Primary Mirror, Diffraction Limited Optics, Rigid
Cast-Aluminum Fork Mount, AutoStar handbox with over 30,000 object library, AutoAlign™, Smart Drive, Periodic Error
Correction (PEC), Standard Field Tripod, AutoStar Suite Astronomer Edition Software, Series 4000 26mm Super Plössl Eyepiece,
Diagonal Prism. AutoStar upgrades available free at www.meade.com.
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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 (Hb) | 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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