In the ever-evolving realm of astrophotography, Celestron has consistently been at the forefront, delivering instruments that bridge the gap between amateur enthusiasm and professional precision. Their latest offering, the Celestron RASA 6-inch (Rowe-Ackermann Schmidt Astrograph), epitomizes this commitment, providing a compact yet powerful tool for capturing the wonders of the night sky.
A revolution in astrophotography
The RASA 6-inch stands as a testament to Celestron’s innovative spirit. This telescope departs from traditional designs, specifically for astrophotography, focusing solely on imaging capabilities. Its compact form factor and cutting-edge optics make it an ideal choice for seasoned astrophotographers and newcomers eager to explore the cosmos.
The RASA (Rowe-Ackermann Schmidt Astrograph) design is a modern evolution of the classic Schmidt camera, engineered specifically for high-speed, wide-field astrophotography. Unlike traditional telescopes, which often prioritize visual observation or slower f-ratios, the RASA is designed with a fast focal ratio of f/2.2, enabling exceptionally short exposure times. This is achieved through a front-mounted camera position that replaces the secondary mirror, allowing light to travel directly from the corrector plate, through a group of rare-earth glass lenses, to the sensor with minimal distortion.
The absence of a secondary mirror also eliminates issues like central obstruction or diffraction spikes, resulting in crisp, high-contrast images. The RASA design offers a flat imaging field and is optimized for APS-C sensors, making it ideal for capturing large portions of the night sky with sharp detail across the entire frame.
Specification
Let us take a look at some of the key specifications of this telescope:
Optical Design: Rowe-Ackermann Schmidt Astrograph
Aperture: 152mm (5.98″)
Focal Length: 335mm (13.18″)
Focal Ratio: f/2.2
Central obstruction diameter: 77mm (3.03″) (46% of aperture diameter)
Light Gathering Power (Compared to human eye): 472x
Resolution (Rayleigh): 0.91 arc seconds
Resolution (Dawes): 0.76 arc seconds
Image Circle: 16mm (0.63″) Ø, 2.74°
Useable field: 22mm (0.86″) Ø, 3.76°, only minimal performance loss at edge of FOV
Wavelength range: 400 – 700 nm
Spot size: < 1.5 μm RMS across image circle
Optical Coatings: StarBright XLT
Off-axis Illumination: 91% at 8mm (0.31″) off-axis
Back focus with included camera adapter: 17.5mm (0.69″)
Optical Tube: Aluminum
Tube Length: 609.6mm (24″)
Optical Tube Diameter: 177.8mm (7″)
Focuser: Standard Schmidt-Cassegrain focuser
Finderscope: Not included
Optical Tube Weight: 8.4 lbs (3.8 kg)
Other Features: Air-cooling system, integrated filter mount
Included items: 42mm (1.65″) T-thread camera adapter, Fan battery pack, Filter drawer with 2″ clear filter
Dovetail: CG-5 Dovetail Bar
Filter Drawer: Accept 2″ format filters, includes 1.25″ filter adapter
Clear Filter: 2″ filter, removable, AR coatings, 2mm glass thickness
Cooling Fan: 12V DC, MagLev
Camera Mounting Threads: M42
Advanced optical design
The RASA’s optical assembly is a marvel of modern engineering:
- Schmidt Corrector Plate: Minimizes spherical aberrations, ensuring sharp images across the field.
- Primary Mirror: Precisely figured to direct light efficiently through the system.
- Lens Group: Comprising rare-earth glass elements, this group corrects for field curvature and chromatic aberrations, delivering true-color renditions of celestial objects.
- Optical Window: A removable 2-inch clear filter maintains peak performance, even when additional filters are introduced.
These components work in harmony to produce images with minimal distortion and exceptional clarity.
User-friendly features
Understanding the needs of astrophotographers, Celestron has incorporated several features to enhance usability:
- Integrated Cooling System: A 12V MagLev fan ensures rapid thermal equilibrium, reducing image distortion caused by temperature differentials.
- Filter Drawer: Accepts both 1.25-inch and 2-inch filters, providing flexibility for various imaging requirements.
- Camera Adapter: The included M42 adapter ensures compatibility with a wide range of astronomical cameras.
These features streamline the imaging process, allowing users to focus on capturing the perfect shot.
Portability meets performance
Weighing in at just 3.8 kg and measuring 24 inches in length, the RASA 6-inch is designed for mobility. Whether setting up in a backyard or traveling to a dark-sky site, this telescope offers the convenience of portability without compromising on imaging capabilities.
Celestron’s proprietary StarBright XLT coatings are applied to all optical surfaces. This multi-layer coating system maximizes light transmission, ensuring that more photons reach the camera sensor. The result is brighter images with improved contrast, essential for capturing the subtle details of deep-sky objects.
Considerations and Limitations
While the RASA 6-inch offers numerous advantages, potential users should be aware of certain considerations:
- Imaging Only: This telescope is designed exclusively for astrophotography and is not suitable for visual observation.
- Camera Compatibility: The design requires the camera to be mounted at the front, which may limit compatibility with certain camera models.
- Field of View: Optimized for sensors up to 22mm diagonal, users with larger sensors may experience vignetting or reduced image quality at the edges.
The Celestron RASA 6-inch represents a significant advancement in accessible astrophotography. Its combination of fast optics, innovative design, and user-centric features makes it a compelling choice for those seeking to delve deeper into the universe through imaging. Whether capturing the delicate filaments of a nebula or the grandeur of a galaxy, the RASA 6-inch stands ready to transform your astrophotography endeavors.
Price and availability
The Celestron RASA 6-inch is available to pre-order for USD 1,699.
Clear skies!
