Features of this Telescope's Optical System . . .
- Oversized primary mirror: The 7" LX200GPS Maksutov has a Pyrex aspheric primary mirror 8.25" in diameter, over an inch larger than the 7" corrector lens at the front of its optical tube that admits the light. Due to the Maksutov design, the meniscus corrector causes the incoming light to diverge as it travels from corrector to primary mirror. If the primary were not oversized, almost 30% of the incoming light would be lost. Despite the 8" diameter of the primary mirror, the 7" diameter of the corrector still determines the aperture of the scope, making this Maksutov a true 7" telescope.
- Meniscus corrector lens: The double-sided spherical meniscus correcting lens is manufactured of Grade-A crown BK7 optical glass and is free of the striations and imperfections that could otherwise degrade optical performance. The BK7 glass provides increased IR and UV transmission for scientific measurement purposes.
- Fully coated optics: The Pyrex primary mirror and secondary mirror spot on the rear of the meniscus corrector are vacuum-coated with a thin layer of aluminum that provides approximately 89% reflectivity per surface. Once aluminized, the mirror surfaces are overcoated with a protective layer of silicon monoxide (quartz) for long life.
A thin layer of anti-reflection magnesium fluoride is vacuum deposited on both sides of the BK7 meniscus corrector to provide a high 98.7% light transmission per surface, compared to the 96% transmission of uncoated glass. Overall light throughput (the amount of light collected by the objective lens that actually reaches your eye or camera) is approximately 77% at the Cassegrain focus.
For those interested in even more brightness for photography and observing faint deep space objects, Meade also offers this scope with optional UHTC (Ultra High Transmission Coatings) for a 15% increase in light throughput. Optional UHTC multicoatings effectively add the equivalent of an extra half inch of light-gathering aperture to the performance of a 7" scope with standard coatings, but with no increase in actual size or weight.
- Fully baffled optics: A conical baffle attached to the correcting lens around the secondary mirror spot, 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 extremely high-contrast images observed against an unusually dark background in lunar, planetary, and deep space observing alike.
- Built-in optics cooling fan: Because the large primary mirror and the thick corrector lens retain heat when you first take the scope outside during cool Fall or Winter nights, a thermal stabilization (cooling) fan is built into the rear cell of the scope. It drastically reduces the time needed to cool the scope optics down to their optimum operating temperature.
- Mirror lock: A progressive tension lock knob on the rear cell locks the telescope's primary mirror rigidly in place once an approximate manual focus has been achieved. The standard equipment electric focuser, described below, is then used for fine focusing. Locking the mirror eliminates the possibility of mirror shift (the image moving from side to side while focusing, caused by the primary mirror tilting on the central baffle tube as the mirror moves fore and aft along the tube). Mirror shift, once the bane of CCD astrophotographers because it could easily move a planetary image off a small CCD chip, is non-existent with the Meade system.
- Electric focuser: The supplied zero image-shift electric microfocuser is controlled by the Autostar II computer hand control. It moves an externally-mounted eyepiece or camera to focus, rather than moving the primary mirror. This eliminates mirror shift during precise image centering and focusing. The microfocuser has four different operating speeds, from very fast down to an extremely slow creep, giving you focusing accuracy to a truly microscopic level during critical visual and astrophotographic applications.
The focuser is designed to hold 2" star diagonals and eyepieces. A supplied 1.25" adapter allows the use of 1.25" diagonals and eyepieces in the 2" focuser. Another supplied adapter duplicates the 2" rear cell thread used on Schmidt-Cassegrain telescopes to allow the use of off-axis guiders, T-adapters, etc. A 1.25" visual back is not supplied with the scope. If you want to do high magnification eyepiece projection photography of the Moon and planets, you will have to add an optional 1.25" visual back #9135 and a tele-extender to the focuser's supplied 2" rear cell thread adapter.