Manual

55
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 eld 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 eld-of-view
signicantly wider than is possible with a standard-size
primary mirror. Note that light ray (2) in the gure would
be lost entirely, except for the oversize primary. It is
this phenomenon which results in Meade ACF having
off-axis eld 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 bafe tube
signicantly increase lunar, planetary, and deep-space
image contrast. These eld stops effectively block off-
axis stray light rays.