Meade-instruments LX600 User Manual download pdf (Page 70)

AutoStar #497 HANDBOX

Appendix J

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

APPENDIX J:

ADVANCED COMA-FREE OPTICS

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 ﬁ 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 ﬁ eld-of-view signiﬁ cantly wider

than is possible with a standard-size primary mirror. Note that

light ray (2) in the ﬁ gure would be lost entirely, except for the

oversize primary. It is this phenomenon which results in Meade

ACF having off-axis ﬁ 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 bafﬂ e tube signiﬁ cantly increase

lunar, planetary, and deep-space image contrast. These ﬁ eld

stops effectively block off-axis stray light rays.

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