Meade LX200GPS-SMT Technical Manual page 3

The Meade Schmidt-Cassegrain Optical System
8.218"
(2)
8.016"
(1)
8.0"
Focal
Plane
In the Schmidt-Cassegrain design of the Meade 8", 10", 12", 14", and 16" LX200GPS models, light enters from the right,
passes through a thin lens with 2-sided aspheric correction ("correcting plate"), proceeds to a spherical primary mirror, and
then to a convex secondary mirror. The convex secondary mirror multiplies the effective focal length of the primary mirror
and results in a focus at the focal plane, with light passing through a central perforation in the primary mirror.
The Meade 8", 10" and 12" Schmidt-Cassegrain models include an oversize primary mirror, yielding a fully illuminated field-
of-view significantly wider than is possible with a standard-size primary mirror. Note that light ray (2) in the figure would be
lost entirely, except for the oversize primary. It is this phenomenon which results in Meade Schmidt-Cassegrains having
off-axis field illuminations about 10% greater, aperture-for-aperture, than other Schmidt-Cassegrains utilizing standard-size
primary mirrors. Field stops machined into the inside-diameter surface of the primary mirror baffle tube significantly
increase lunar, planetary, and deep-space image contrast. These field stops effectively block off-axis stray light rays.
The Meade Maksutov-Cassegrain Optical System
The Meade 7" (178mm) Maksutov-Cassegrain Optical System
8.25"
Focal
Plane
The Meade 7" Maksutov-Cassegrain design optimizes imaging performance by utilizing a combination of a two-sided
spherical meniscus lens (right), a strongly aspheric f/2.5 primary mirror, and a spherical secondary mirror. The convex sec-
ondary mirror multiplies the effective focal length of the primary by a factor of six, resulting in an overall a focal length of
2670mm and a focal ratio of f/15 system at the Cassegrain focus.
The oversize 8.25" primary mirror results in a fully-illuminated (unvignetted) field of view significantly wider than can be
obtained with Maksutov optics incorporating primary mirrors of the same aperture as their meniscus correcting lenses.
Computer-optimized primary and secondary mirror baffles, as well as a sequence of field stops internal to the primary mir-
ror baffle, yield lunar, planetary, stellar, and deep-space images of uncommonly high contrast and resolution.
(2)
(1)
Ray (1)
Primary Baffle Tube
Field Stops
Primary Mirror
Field Stops
Primary Baffle Tube
Primary Mirror (f/2.5)
(1)
(2)
Ray (2)
1/2
Secondary
Mirror
Secondary
Baffle
Correcting
Plate
(8" model depicted in diagram. Not to scale.)
Secondary Baffle
8.0"
7"
Meniscus
Lens
(Diagram not to scale)