Tuesday, April 8, 2008

Maksutov-Cassegrain: New Market Leader

Like the Schmidt-Cassegrain telescopes, the Maksutov-Cassegrain is a catadioptric design; however, these newer instruments optimize imaging performance by combining a special spherical meniscus (concave) lens with two mirrors. The secondary mirror multiplies the focal length of the telescope. The combined effect of the concave lens, the aspherical primary mirror, and the convex secondary mirror produces a telescope that is almost as well suited to lunar and planetary observation as a refractor, yet it has many of the reflector’s advantages for deep-space viewing. These qualities are similar to the conventional Schmidt-Cassegrain design, but the Maksutov-Cassegrain variation tends to yield images of greater contrast than one gets from telescopes of the earlier design.

A 7-inch Maksutov is significantly more expensive than an 8-inch Schmidt-Cassegrain; however, Meade has marketed for some years now two extremely popular small Maksutov models, the ETX-90EC and ETX-125EC (90 mm and 125 mm, respectively), which trade aperture for price. The 90-mm model can be purchased for under $500, and the 125-mm model for less than $900.

Diagram of a Maksutov-Cassegrain telescope. Light enters the concave lens at the right and is reflected by the aspheric primary mirror at the left, which sends it back to the spherical secondary mirror on the right. This, in turn, focuses the image on the focal plane on the left.

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