Meade Instruments LX850 - Manual (Page 55)

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Appendix E
ADVANCED COMA-FREE OPTICAL SYSTEM
APPENDIX E:
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 shown above, 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.
The Meade ACF optical system includes an oversized
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 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.