Meade LX90 - Page 2

Primary Baffle Tube
Field Stops
Primary Mirror
Ray (1)
Ray (2)
(2)
(1)
(2)
(1)
Secondary
Mirror
Correcting
Plate
S
econdary
B
affle
(2)
(1)
F
ocal
P
lane
In the Schmidt-Casseg
rain design of the Meade LX90, light enters from the right, passes through a thin lens with 2-sided
aspher
ic 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" LX90 Schmidt-Cassegrain includes an oversize primary mirror of an 8.25" diameter, yielding a fully illumi-
nated field-of-view significantly wider than is possible with a standard-size primary mirror. Note that light ray (2) in the fig-
ure 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 Schmidt-Cassegrain Optical System