Out on the observing field, Vixen's 8-incher appears to be just another SCT. A close look shows several differences. First, rather than gray, blue, or orange, its OTA is a striking white. Also, it seems to be missing its corrector. It is not a classical
Cassegrain, however. Like the OMC MCTs, it is a subaperture corrector member of the MCT family. The Vixen's particular optical recipe is a little different from that of the Orions, being based on the Shafer-Maksutov design. Otherwise, we are in familiar territory. It has a focal ratio of f/9.75, close to the standard f/10 of the friendly neighborhood SCT. Unlike SCTs, however, the VMCs do not move the primary mirror to focus, and are equipped with a standard rack and pinion focuser on the rear cell. The rear port, though it looks like it should be SCT accessory compatible, is actually a T-mount affair. It should be fairly easy to find adapter rings to hang just about anything on this CAT's port, however.
The VMC is solidly built and quite good optically, something typical for this Japanese manufacturer's telescopes. The only question here is, "Why?" Its performance is nearly identical to the average SCT OTA, but at a price about $300 higher— the Vixen OTA is currently priced at $1,300. Why isn't the VMC better than the less-expensive SCTs? That may have something to do with the fact that the telescope's central obstruction is close to 30%. Or, it may be because it is harder to get the subaperture corrector "just right" than it is to do a good full-aperture lens. Unlike a full-aperture corrector, light must pass through the VMC's lens twice since it is mounted in front of the secondary. This small corrector does reduce the dew and weight problems of full-aperture MCT and SCT correctors. What is one thing some imagers do not like about this CAT? Since there is no corrector lens on the front to support a secondary mirror, the secondary/corrector assembly is held in place by "spider" vanes. These cause prominent diffraction spikes around stars in astrophotos.
In addition to the VMC200L 8-inch, Vixen also makes a 10-inch aperture version of this design, the f/11.5 VMC260L, and another subaperture scope, one intended primarily for imaging, the VC200L, an f/9 8-inch that uses an aspheric primary mirror and a three-element corrector mounted in front of and in contact with the secondary.
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