Meade LX850-ACF 10 inch User Manual - Page 55

Appendix E APPENDIX E: ADVANCED COMA-FREE OPTICAL SYSTEM (2) (1) Focal Plane (2) (1) (1) (2) Ray (2) Ray (1) Primary Baffle Tube Field Stops Primary Mirror Secondary Mirror Correcting Plate Secondary Baffle 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, aperturefor-aperture, than other systems utilizing standard-size primary mirrors. Field stops machined into the insidediameter surface of the primary mirror baffle tube significantly increase lunar, planetary, and deep-space image contrast. These field stops effectively block offaxis stray light rays. 55