• Low thermal expansion mirrors: The primary and secondary mirrors are made of low thermal expansion Pyrex to limit the possibility of the focal length changing as the temperature drops. This reduces the possibility of the focus changing during critical through-the-scope CCD imaging.
  

• Oversized primary mirrors: The diameter of the primary mirror of each ETX-LS is larger than the diameter of the corrector lens at the front of its optical tube that admits the light. For example, the primary mirror of the 8" scope is actually 8.25" in diameter, compared to the 8" diameter of the corrector lens. 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 low thermal expansion primary and secondary Pyrex mirrors are vacuum-coated with aluminum that is enhanced with multiple layers of titanium dioxide and silicon dioxide for increased reflectivity. These multicoatings are then overcoated with a protective layer of silicon monoxide (quartz) for long life.
  
      A series of anti-reflective coatings of aluminum oxide, titanium dioxide, and magnesium fluoride are vacuum-deposited on both sides of the Schmidt 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 (the amount of light collected by the objective that actually reaches your eye or camera), when compared with standard coatings. For example, they effectively add the equivalent of a little more than four-tenths of an inch of extra light-gathering aperture to the performance of the 6" optical system - but with no increase in actual size or weight. The UHTC multicoatings 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 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 baffle tube. The result of these baffle systems is improved contrast in lunar, planetary, and deep space observing alike.