Orion‘s 6 and 7-inch Maksutov-Cassegrainians are a good alternative for lunar, planetary, and double star observers who desire a very capable instrument without the high price of of a mid-size apochromatic refractor.
Both the 6 and 7-inchers are stubby and rather hefty scopes weighing in at 12 and 16 pounds respectively. Recent upgrades have provided 2-inch visual backs, but no finder, star diagonal or eyepiece is included.
Sky-Watcher offers an identical optical system with a different color scheme and full complement of accessories at a higher price, and Celestron sells the 7-inch with Starbright XLT coatings that provide additional light throughput.
Both telescopes could be considered specialist instruments optimized for high magnifications at the expense of rich-field performance. The secondary obstruction of the 6-inch, f/12, is comparable to that of a typical Schmidt-Cass, and the f/15, 7-inch is only about 28 percent when the secondary baffle is included.
The result is tight, high-contrast images that that are almost (but not quite) refractor-like. Multiple stars such as Castor and Iota Cass are neatly resolved and not unlike the views created by a Takahashi 128mm fluorite refractor, but with a larger first diffraction ring. Mars displays significant surface detail, limb brightenings and polar caps at 250x in the 6-inch and 300x plus with the larger scope.
Lunar detail is likewise sharp, detailed and completely free of false color.
Deep sky performance is limited by the long focal ratios, but the dark sky background and tight star rendition is pleasing and impressive on brighter objects such as the Orion Nebula.
There is a downside: Cool-down times are long because of the thick meniscus lens, and both scopes showed significant image shift with their moving-mirror focus mechanism.
On balance, however, both telescopes represent an excellent value for the money.
The good: Fine optical quality, reasonable price
The bad: Long cool-down time, rather heavy
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