Features of this Optical Tube's Optical System . . .

• Advanced Coma-Free catadioptric designed to emulate the optical performance of a Ritchey-Chrétien telescope: The traditional two-mirror Ritchey-Chrétien (RC) design uses hyperbolic primary and secondary mirrors to produce images that are free from coma over a wide field. Because of this wide coma-free field and a relatively fast focal ratio, the Ritchey-Chrétien design is particularly well suited to astrophotography. The RC is the design of choice for most of the major professional observatory telescopes built in the last half-century. For example, the Hubble Space Telescope and the twin 10-meter Keck telescopes in Hawaii are Ritchey-Chrétiens.
  

      However, fabricating and testing a large aperture hyperbolic mirror is a very complex task (just ask the people who built the initially-flawed, with the flaw not discovered until it was in space, Hubble Space Telescope). That is why traditional two-mirror Ritchey-Chrétiens are expensive to manufacture and purchase, often too expensive for many amateur astronomers.
  

      To emulate the coma-free performance of a true RC telescope, while keeping the cost within reason, the Meade Advanced Coma-Free (ACF) catadioptric optical system uses a full aperture aspheric corrector lens in conjunction with a simple spherical primary mirror. This creates a two-element primary mirror system that performs like an RC's single hyperbolic primary mirror from the optical point of view of the secondary mirror.
  

      The hyperbolic secondary mirror itself is mounted directly on the rear of the corrector lens, rather than in the traditional RC's conventional spider vane assembly. This eliminates the image-degrading diffraction spikes of the secondary mirror support structure visible in commercial RC scope images. The result is RC-class coma-free wide-field performance, at about a fourth the cost of most true RC systems.
  

      The corrector-modified design would itself be expensive to fabricate were it not for Meade's more than a quarter-century of experience making Schmidt-Cassegrain correctors, which are in the same optical family as the corrector needed for the coma-free design of this optical tube. An additional benefit of the full aperture corrector in the ACF design is slightly better correction for astigmatism than the traditional RC design.
  

      In addition, an ACF optical system, due to its front corrector plate, is a closed tube design. This keeps the primary optical components protected from dust, moisture and other contaminants that might fall on the optical surfaces of the primary and secondary mirrors as can happen with the traditional open-tube RC design.
  

      While an ACF optical system may not be a traditional RC design, its performance is RC-like in all important characteristics. A review in Sky & Telescope magazine of the predecessor of the Meade ACF optics said the bottom line is that the optics do "indeed perform like a Ritchey-Chrétien." Another such review, in Astronomy magazine said, "This scope delivers Ritchey-Chrétien-like performance at a fraction of the cost."
  

• Oversized primary mirror: The diameter of the primary mirror of each ACF optical tube is larger than the diameter of the corrector lens at the front of its optical tube that admits the light. The primary mirror of the 8" scope is actually 8.25" in diameter, compared to the 8" diameter of the corrector lens. The 10" primary is 10.375" in diameter; the 12" is 12.375"; the 14" is 14.57"; and the 16" primary is 16.375" in diameter. Oversizing the primary mirror in this way gives you a wider fully-illuminated field than a conventional catadioptric scope whose corrector and primary mirror are the same size. The result is a gain of 5% to 8% more off-axis light available to your eye or camera, depending on the telescope model.
  

• Fully multicoated UHTC (Ultra High Transmission Coatings) optics: The primary and secondary mirrors are vacuum-coated with aluminum, enhanced with multiple layers of titanium dioxide and silicon dioxide for increased reflectivity. A overcoating layer of durable silicon monoxide (quartz) assures long life.
  

      A series of anti-reflective coatings of aluminum oxide, titanium dioxide, and magnesium fluoride are vacuum-deposited on both sides of the full aperture corrector plate. These antireflection multicoatings provide a high 99.8% light transmission per surface, versus a per-surface transmission of 98.7% for standard single-layer coatings.
  

      UHTC multicoatings provide a 15% increase in light throughput compared with standard single-layer coatings. They effectively add the equivalent of 15% extra light-gathering area to the performance of a scope with standard coatings. It's the equivalent of three-quarters of an inch of extra aperture in the case of a 10" scope, for example, but with no increase in actual size or weight. UHTC coatings also improve contrast, for lunar and planetary images that appear sharper and more crisply defined.
  

• Fully baffled optics: A cylindrical baffle around the secondary mirror, in combination with the cylindrical baffle tube projecting from the center of the primary mirror, prevents stray off-axis light from reaching the image plane. In addition, a series of field stops machined into the inner surface of the central baffle tube effectively eliminates undesirable light which might reflect from the inside surface of the tube. The result of these baffle systems is improved contrast in lunar, planetary, and deep space observing alike.
  

• Mirror lock: A progressive tension lock knob on the rear cell locks the telescope's primary mirror rigidly in place once a photographic manual focus has been achieved. Locking the mirror eliminates the possibility of mirror shift (the image moving from side to side as the optical tube passes from one side of the zenith to the other). Mirror shift, once the bane of CCD astrophotographers because it could blur the image without the astrophotographer being aware of it until the image was examined later during the processing stage, is non-existent with the Meade system.