Meade LNT Instruction Manual download pdf (Page 2)

Primary Baffle Tube

Field Stops

Primary Mirror

Ray (1)

Ray (2)

(2)

(1)

(2)

(1)

Secondary

Mirror

Correcting

Plate

econdary

affle

(2)

(1)

ocal

lane

In the Schmidt-Casseg

rain design of the Meade LX90, light enters from the right, passes through a thin lens with 2-sided

aspher

ic 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.

The Meade 8" LX90 Schmidt-Cassegrain includes an oversize primary mirror of an 8.25" diameter, yielding a fully illumi-

nated field-of-view significantly wider than is possible with a standard-size primary mirror. Note that light ray (2) in the fig-

ure 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

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Meade LNT Instruction Manual Page 2