Celestron CGEM II 700 Maksutov-Cassegrain Telescope

A 180mm f/15 System for High-Contrast Planetary Views

The Maksutov-Cassegrain design is engineered for superior contrast, making it a specialized instrument for detailed solar system and small deep-sky observation. The long f/15 focal ratio darkens the sky background and provides high magnification for resolving features like Jupiter's cloud bands, Saturn's rings, and fine lunar craters. Its optical system produces bright, sharp images that are virtually free of chromatic aberration.

A key advantage of the Mak design is its "secondary spot," a reflective coating applied directly to the corrector lens. This results in a tiny central obstruction of just 5% by area, significantly less than a comparable Schmidt-Cassegrain, which is the source of its signature high-contrast views. This design also means the telescope does not require periodic collimation. The primary trade-off is that the thick 180mm corrector plate requires a longer cool-down time to acclimate to ambient temperatures.

CGEM II Mount: 40 lb Payload Capacity and Meridian-Crossing Stability

The CGEM II mount provides the rigid, vibration-free foundation necessary for high-magnification viewing and imaging. Its 40 lbs instrument load capacity easily supports the 19 lbs optical tube, leaving over 20 lbs of capacity for cameras, guide scopes, and other accessories. The tripod features 2" diameter steel legs with graduated markings for easy, repeatable setup.

Designed for astrophotography, the mount incorporates low cog DC servo motors with integrated optical encoders for smooth, accurate tracking. For imagers, the CGEM II can track an object up to 20° past the meridian before a meridian flip is required, allowing you to capture data during the best part of the night. All motor and accessory cabling is housed internally, preventing snags and simplifying setup and breakdown.

GoTo & Tracking: All-Star Alignment and Permanent Periodic Error Correction

At the heart of the system is the NexStar+ hand controller, giving you access to a database of over 40,000 celestial objects. The mount's GoTo system is complemented by Celestron's innovative All-Star Polar Alignment procedure, which allows for a quick and accurate alignment using any bright star, even if Polaris is not visible. This process typically takes only 15 minutes.

For long-exposure imaging, tracking accuracy is critical. The CGEM II features Permanent Periodic Error Correction (PPEC), which allows you to record and correct for the inherent periodic errors in the worm gears. Once recorded, the correction is stored in the mount's memory. For the most demanding applications, a dedicated autoguide port allows the connection of an autoguiding camera to achieve sub-arcsecond tracking precision.

CGEM II 700 Mak vs. 8" SCT: The High-Contrast Specialist

When choosing between this 7" Maksutov and a more conventional 8" Schmidt-Cassegrain (SCT) on the same mount, the decision comes down to your primary targets.

• The 8" SCT's Advantage: An 8" SCT gathers more light and typically operates at a faster f/10 focal ratio. This gives it an edge for viewing and imaging larger, fainter deep-sky objects like galaxies and large nebulae, where its wider field of view is a benefit.
• The 7" Mak's Advantage: The CGEM II 700 Mak is the specialist. Its f/15 focal ratio and exceptionally small 5% central obstruction deliver noticeably higher contrast on bright objects. This makes it the superior choice for resolving subtle details on planets, separating tight double stars, and exploring the lunar surface at high power. It also holds collimation indefinitely, a significant convenience.