Celestron RASA 6" OTA

The 152mm f/2.2 RASA Optical System

At the heart of the RASA 6 is a patented optical design engineered for one purpose: capturing stunning astroimages with unparalleled speed. The f/2.2 focal ratio gathers light 472x faster than the human eye, allowing you to capture faint details in galaxies and nebulae with sub-exposures that are minutes, not hours, long. The system uses a Schmidt corrector, primary mirror, and a 3-element lens group with StarBright XLT coatings to deliver sharp, coma-free stars across its 16mm optimized image circle.

Integrated Filter Drawer and 12V Cooling System

The RASA 6 is built for the modern imager with features that streamline your workflow. An integrated filter drawer accepts both 2" and 1.25" filters, allowing you to easily switch between broadband and narrowband targets without disassembling your camera setup. A 12V DC MagLev fan actively cools the optics to ambient temperature, minimizing thermal noise and ensuring your images are as clean as possible.

An 8.4 lb Portable Astrograph with a CG-5 Dovetail

Designed for both backyard and dark-site imaging, the RASA 6 is exceptionally portable. The aluminum optical tube is just 500.5mm long and weighs only 8.4 lbs, making it compatible with a wide range of mid-sized equatorial mounts. It attaches securely via a standard CG-5 dovetail bar, and the included M42 T-thread adapter provides a standard 17.5mm back focus distance for most modern CMOS and CCD astronomy cameras.

Short Exposures and a 22mm Useable Field

The RASA 6's speed fundamentally changes the imaging experience, enabling a near-real-time view of the deep sky when paired with sensitive cameras and live-stacking software. The optical design provides a 22mm useable field, corresponding to a 3.76° swath of the sky—wide enough to frame large targets like the North America Nebula (NGC 7000). The trade-off for this speed is a significant 46% central obstruction, which reduces contrast on high-resolution planetary targets but is ideal for deep-sky objects where light-gathering is paramount.

RASA 6 vs. Slower Refractors: The f/2.2 Advantage

Compared to a comparably priced apochromatic refractor, the RASA 6 offers a distinct set of advantages for deep-sky imaging. While a refractor may offer higher contrast for visual use, the RASA 6's f/2.2 focal ratio is drastically faster than the typical f/6 or f/7 of a refractor.

• Exposure Speed: An f/2.2 system captures an image approximately 8-10 times faster than an f/7 system, meaning a 30-second RASA exposure is equivalent to a 4-5 minute exposure on a typical refractor.
• Tracking Demands: Shorter exposures significantly reduce the demands on your mount's tracking accuracy, often eliminating the need for an autoguider and simplifying your entire setup.
• Resolution: With a Dawes' limit of 0.76 arc seconds, the RASA 6 out-resolves many smaller refractors, revealing finer details in distant galaxies and planetary nebulae.