Primary Baffle Tube
Field Stops
Primary Mirror
Ray (1)
Ray (2)
(2)
(1)
(2)
(1)
Secondary
Mirror
Correcting
Plate
Secondary
Baffle
(2)
(1)
Focal
Plane
Unlike Schmidt-Cassegrain systems, Meade’s Advanced Coma-Free (ACF)
optical system provides razor-sharp pin-point star images all the way to the
very edge of the field of view. This aplanatic (coma-free) optical system brings
the highest level of performance to the amateur astronomer.
In the ACF design of the Meade LX90, 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 hyperbolic secondary
mirror. The hyperbolic 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.
All models of the Meade LX90-ACF includes oversize primary mirrors,
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 ACF having off-axis field illuminations about 10% greater,
aperture-for-aperture, than other systems 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 Advanced Coma-Free Optical System
56
APPENDIX D: CATADIOPTIC
OPTICAL SYSTEMS
Primary Baffle Tube
Field Stops
Primary Mirror
Ray (1)
Ray (2)
(2)
(1)
(2)
(1)
Secondary
Mirror
Correcting
Plate
Secondary
Baffle
(2)
(1)
Focal
Plane
In the Schmidt-Cassegrain design of the Meade LX90, 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.
All models of the Meade LX90 Schmidt-Cassegrain includes oversize
primary mirrors, 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 Schmidt-Cassegrain Optical System
Summary of Contents for LX90-ACF Advanced Coma-Free
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