Rigel Systems RS-Spectroscope

The RS-Spectroscope by Rigel Systems is a compact astronomical accessory designed to open a new dimension in amateur observation. Unlike traditional visual astronomy, which is limited to brightness, motion, and general color, spectroscopy allows users to examine the composition and physical properties of stars and nebulae. Priced at $329.95, this device makes it possible to observe the spectrum of light emitted by celestial objects, a method that forms the foundation of astrophysics. By attaching to the eyepiece of a telescope, the RS-Spectroscope spreads starlight into a full visible spectrum, allowing observers to see both emission and absorption lines that indicate the chemical makeup of astronomical sources.

Exploring astronomical spectra: Rigel Systems RS-Spectroscope

At its core, the RS-Spectroscope functions as an inline spectroscopic tool, featuring a grating element that diffracts light and a widening lens that enhances spectral detail. When observing bright stars such as Sirius or Vega, users will see a rainbow of colors interrupted by fine, dark vertical lines. These absorption lines are the result of specific elements in the star's atmosphere absorbing certain wavelengths of light, effectively imprinting a chemical fingerprint onto the spectrum. Observing and identifying these lines connects users directly with the physical processes taking place in distant stellar atmospheres. The RS-Spectroscope is designed not just for viewing, but also for capturing these phenomena using standard digital and DSLR cameras.

Attaching the RS-Spectroscope is a straightforward process. It fits onto most 1.25-inch eyepieces, particularly those with long eye relief and flat or rubber eyecup tops. Eyepieces with longer focal lengths, such as 25mm to 55mm, tend to produce the most usable results, as they offer low magnification and wide fields, both helpful for observing and imaging spectra. The spectroscope’s grating is tilted at approximately 23 degrees, causing the dispersed spectrum to exit at an angle from the zero-order image. When aligned correctly, users can view the star in its normal position and then shift their eye slightly to see the full spectral spread.

The RS-Spectroscope is engineered for both visual and photographic applications. When used visually, users begin by focusing a bright star with the bare eyepiece. After attaching the spectroscope, they lean to view the first-order spectrum, which appears off-center due to the diffraction angle. If properly focused, the spectral lines will be sharp and distinct. The widening lens is especially important in this process. Without it, features may appear compressed and difficult to resolve. With the widening lens in place, fine structures within the spectrum become much more visible, enhancing contrast and helping the eye distinguish individual lines.

Spectroscopy relies heavily on atmospheric conditions. Known as "seeing," the stability of the air significantly impacts the clarity of spectral features. On nights with good seeing, stars appear sharp and steady, making their spectral lines clean and well defined. On poor nights, with turbulent or unstable air, the lines may appear wavy, distorted, or entirely obscured. This effect is not a flaw in the instrument but a reflection of atmospheric interference. The RS-Spectroscope can be used effectively during moderate conditions, but best results occur on calm, stable nights.

In photographic applications, the RS-Spectroscope supports two primary techniques: drift spectroscopy and streak spectroscopy. Drift spectroscopy involves disabling the telescope’s clock drive, allowing the star to slowly move across the field during exposure. This drift widens the spectrum naturally and enhances the visibility of absorption and emission lines. A standard setup using a DSLR might include an 8-second exposure at ISO 800 with a zoom setting around 70mm. The result is a broadened spectral image showing distinct vertical lines, ideal for analysis and display. To ensure proper focus, observers adjust until the blue end of the spectrum widens first, followed by the red, a consequence of the grating’s stronger bending of shorter wavelengths.

Streak spectroscopy, in contrast, keeps the drive on and allows the star to remain fixed. This method produces a tighter, brighter spectrum but often at the cost of line resolution. The benefit lies in collecting more photons per pixel, which helps in cases of fainter stars or low signal-to-noise ratios. While drift spectroscopy reveals fine detail, streak spectroscopy offers a practical alternative for dimmer targets or faster imaging sessions.

The RS-Spectroscope attaches to an eyepiece to spread light from Stars and Nebulae into a rainbow of colors

Using the RS-Spectroscope with a digital camera involves mounting the camera at the appropriate distance and orientation relative to the spectroscope and eyepiece. In DSLR configurations, the telescope does not operate at prime focus. Instead, the eyepiece remains in the optical train to collimate light before it reaches the diffraction grating. The DSLR lens is then used to refocus the dispersed light onto the camera sensor. Rigel Systems offers accessories such as the QuikAdapt to aid in positioning and stabilization. Users can fine-tune camera placement vertically and rotationally to align the spectrum with the long axis of the camera sensor.

For best results, camera settings should be optimized based on target brightness. Brighter stars require shorter exposures and lower ISO settings, while dimmer targets may call for longer integrations and higher sensitivity. Canon DSLRs, for example, can be operated via remote control software that allows full manual adjustment. It is strongly recommended to shoot in RAW format, as JPEG compression artifacts tend to degrade the clarity of spectral lines. RAW files also offer greater flexibility in post-processing, where users can enhance contrast, adjust skew and rotation, and isolate spectral features for study.

Image processing plays a critical role in producing high-quality spectroscopic data. Rigel Systems suggests a combination of proprietary and free tools. RAW images are typically converted to TIFF, then cropped, rotated, and deskewed using software like Photoshop. A continuum image is created by blurring the spectrum along the direction of dispersion, then subtracted from the original to isolate the spectral lines. Further contrast adjustments reveal fine details that may not be visible in the raw capture. While this workflow requires time and experience, the results can rival those from more expensive, dedicated spectroscopy equipment.

A notable enhancement to the RS-Spectroscope system is the use of a telecompressor. When properly spaced, a telecompressor reduces the effective focal length of the system, thereby compressing the spectrum’s width and increasing its brightness. This not only improves signal quality but also reduces the impact of poor seeing by minimizing the apparent size and movement of the star image. Photographs of stars like Arcturus show that a properly implemented telecompressor can significantly improve spectral sharpness and contrast while also allowing smaller telescopes to match the performance of larger ones.

Decoding the message in starlight

The RS-Spectroscope is also capable of observing emission line spectra from nebulae. Unlike stars, which produce continuous spectra with dark absorption lines, planetary nebulae emit light at specific wavelengths. This causes them to appear as distinct, colored spots along the spectrum when observed through the RS-Spectroscope. For instance, the Ring Nebula (M57) produces visible emissions in the green-blue part of the spectrum, particularly in the doubly ionized oxygen (O III) lines. By stacking multiple long exposures, observers can capture nebular spectra even at relatively faint magnitudes, making this tool valuable for studying non-stellar sources as well.

The mechanical design of the RS-Spectroscope is straightforward but effective. The main housing secures to the eyepiece using three thumb screws, allowing it to grip the rubber eyecup groove or the top rim. For smaller eyepieces, longer screws are provided. The widening lens inserts into the grating module, with alignment aided by visual marks. The internal diffraction grating is protected by a microglass window, which should be handled with care. Maintenance is minimal, limited to occasional dusting with a soft brush or air blower. Rigel Systems recommends storing the device in a safe, dry location and avoiding impact to the optical surfaces.

Despite its simple construction, the RS-Spectroscope is a highly functional instrument. Its educational potential is considerable. Students and amateur astronomers can visually explore the stellar classification system known as the OBAFGKM sequence, identifying the spectral fingerprints that separate hot blue stars from cooler red giants. The spectroscope also offers a tangible way to understand the Hertzsprung-Russell diagram, a foundational concept in stellar evolution, by linking observed spectra to physical parameters like temperature and luminosity.

The RS-Spectroscope is not without limitations. Its performance depends heavily on seeing conditions, precise alignment, and the optical quality of the telescope and eyepiece used. It is best suited for telescopes with good star images and sufficient aperture to gather enough light for detailed spectral capture. Users must also be comfortable with handling camera equipment and post-processing techniques to extract the full potential of the system. While it is designed to be accessible, the RS-Spectroscope is a tool that rewards patience and experimentation.

In terms of value, the RS-Spectroscope offers an affordable entry point into real astronomical spectroscopy. At a fraction of the cost of professional or research-grade systems, it enables meaningful scientific observation and engagement with astrophysical phenomena. Whether for educational demonstrations, outreach programs, personal exploration, or photographic documentation, it provides a versatile and portable solution for those interested in going beyond traditional stargazing.

These spectra were photographed in color in 8 seconds, unguided

In conclusion, the RS-Spectroscope from Rigel Systems brings the science of spectroscopy within reach of amateur astronomers. Its ability to reveal the hidden structure of starlight transforms the telescope from a simple magnifier into a diagnostic instrument. With thoughtful use and careful attention to detail, observers can uncover the chemical and physical secrets of stars, nebulae, and other celestial objects. For anyone seeking a deeper connection to the universe through hands-on investigation, the RS-Spectroscope offers a compelling and educational pathway into the world of astronomical spectroscopy.