Rowe-Ackermann Schmidt Astrograph (RASA)
The Rowe-Ackermann Schmidt Astrograph (RASA) is a specialized type of astrograph, designed and manufactured by Celestron, that focuses on high-resolution wide-angle astrophotography. This astrograph is unique in its ability to collect light quickly, allowing deep space photography with exceptional sharpness and detail.
Structure and optical design:
RASA combines elements of the Schmidt-Cassegrain telescope and astrograph to achieve optimized astrophotographic quality. Key components include:
- Primary mirror: A large parabolic mirror that collects and focuses light. The large aperture ensures fast light collection.
- Schmidt correction plate: An aspherical plate located on the front that corrects spherical aberration and ensures a sharp and even image.
- Built-in correction optics: Includes lenses placed between the primary mirror and the camera to minimize optical defects such as coma and image distortion.
- Front-mounted focal plane: Unlike traditional telescopes, the focal plane is located in front of the corrector plate, allowing the camera to be attached directly to the front of the instrument.
Operating principle:
Light enters the RASA through the front correction plate, which corrects for spherical aberration and focuses the light onto the parabolic primary mirror. The light is then reflected back into the integrated optics, which include correction lenses that eliminate optical defects and produce a flat and sharp field of view.
Key features and benefits:
- Fast aperture (f/2). This makes it ideal for astrophotography when you need to capture fine details in space such as nebulae, star clusters and galaxies.
- Wide-angle field of view: Due to its design, the RASA provides a wide field of view, making it ideal for photographing large areas of the night sky with high resolution.
- High image quality: Correction lenses eliminate defects such as coma and distortion, ensuring a sharp image from the center to the edges of the frame.
- Fast and efficient camera mounting: the front-mounted focal plane allows easy attachment of astrophotography cameras, minimizing the number of elements between the camera and optics and reducing light loss.
Limitations and challenges:
- Not designed for visual observation: the RASA is designed for photographic purposes only and is not suitable for visual observation because it does not have an eyepiece output.
- Complicated accessory handling: Due to the camera's location at the front of the telescope, access to other accessories may beaccessories may be more limited and handling of mounting or focusing may be more difficult.
- High collimation requirements: as with most advanced optical systems, it is important to have the RASA properly collimated to achieve optimal results.
Typical applications:
RASA is ideal for astrophotographers who want to capture large areas of the night sky in extraordinary detail. It is suitable for:
- Photographing nebulae and large areas of the Milky Way.
- High-resolution astrophotography focusing on deep space objects.
- Imaging comets and other large objects where a wide field of view is needed.
Popular models:
Celestron offers several versions of the RASA, including 8" and 11" models that are designed to meet the varying needs of astrophotographers. Larger models allow for even faster light gathering and provide higher resolution.
The Rowe-Ackermann Schmidt Astrograph (RASA) represents the technological pinnacle of astrophotography. Its combination of speed, wide field of view and optical quality make it the ideal tool for capturing beautiful and detailed images of the night sky.