For solar astronomy enthusiasts, imaging the Sun in detail beyond the white-light photosphere has always required specialized equipment. While hydrogen-alpha filters dominate the amateur solar imaging scene, a newer alternative has been quietly gaining traction – spectroheliographs. And leading this new wave of instruments is the MLAstro SHG 700, a fully pre-assembled, high-resolution solar spectroheliograph designed specifically for astrophotographers. In this article, we dive into what makes the SHG 700 unique, how it works, and why it’s becoming a serious contender against traditional etalon-based systems.
What is a spectroheliograph?
A spectroheliograph is an optical instrument used to image the Sun in a very narrow band of light, isolating specific wavelengths emitted by elements such as hydrogen (H-alpha), calcium (Ca K), or sodium (Na D). While etalons isolate a particular wavelength across the entire solar disk in real-time, spectroheliographs take a different approach.
In an SHG, the Sun’s image is scanned line-by-line through a narrow slit. A diffraction grating disperses the light into its spectrum, and a camera captures the specific wavelength selected. The result is a monochromatic image built from thousands of spectral slices, each representing a narrow slice of the Sun at a specific wavelength. Specialized software later reconstructs a complete image from the scan. This technique, although more involved, offers significant advantages in terms of spectral resolution and wavelength flexibility.
Introducing the MLAstro SHG 700
The MLAstro SHG 700 is one of the most advanced spectroheliographs available to the amateur astronomy community. Unlike DIY setups, which require extensive knowledge of optics and painstaking alignment, the SHG 700 arrives pre-assembled, calibrated, and ready to use.
Its design is compact but robust, featuring a CNC-machined aluminum housing that maintains mechanical stability even during long imaging sessions under the Sun. The unit includes:
- 2x MLAstro 72mm flat-field compound lenses
- 1x 2400 l/mm, 25x25x6mm holographic grating
- 1x 7mm long, 7-micron wide Quartz slit
This configuration enables full-disk solar scans for telescopes with focal lengths up to 730 mm, making it compatible with most small to medium-sized refractors.
How it works
The imaging workflow involves scanning the solar disk using motorized tracking (RA drive or a manual scan). As sunlight passes through the quartz slit, it is collimated, diffracted, and re-imaged onto a fast monochrome camera. This camera captures individual spectral lines, usually in H-alpha, though other lines like Ca K and He D3 are also possible.
Once scanning is complete, software like SHG GUI or Intensitygram combines the spectral slices into a full image. Users can then apply image processing techniques similar to those used in planetary imaging – stacking, sharpening, and contrast enhancement—to produce stunning final results. The system’s resolution is exceptional. It offers a spectral sampling of around 0.06–0.1 Å per pixel, much narrower than most commercial etalon filters, which typically sit around 0.5–0.7 Å full width at half maximum (FWHM).
Etalon vs. spectroheliograph: What’s the difference?
Etalon-based systems, such as those from Daystar, Lunt, and Coronado, are popular due to their ease of use and real-time imaging. These systems use interference filters to transmit a narrow band of light, typically centered on the H-alpha line (656.28 nm), and can show prominences, filaments, and surface activity in real time. However, etalons have several limitations. Their bandwidth is fixed and often broader than what a spectroheliograph can resolve. Moreover, high-quality etalons are expensive—often costing several thousand dollars—and are sensitive to temperature and tilt, which can affect the uniformity and quality of the image.
The MLAstro SHG 700, in contrast, uses no interference filters. It resolves much narrower spectral features and can be tuned digitally to any wavelength within the visible range. This flexibility allows users to explore not just hydrogen-alpha, but other lines like Ca II K (393.4 nm) and sodium D (589.3 nm), giving broader scientific and aesthetic utility. While SHGs cannot provide live video feeds due to their scanning nature, the trade-off is a significantly higher spectral resolution and the ability to switch wavelengths at no extra cost.
Designed for simplicity and precision
One of the most appealing aspects of the SHG 700 is its plug-and-play nature. Unlike traditional SHGs that require careful optical alignment, this instrument arrives fully aligned and tested. It’s a major step forward in making spectroheliography accessible to a broader audience.
The optics are custom-designed and provide sharp imaging across a 16 mm illuminated field—more than sufficient for common CMOS sensors. The internal layout ensures the slit, lenses, and grating remain fixed and orthogonal, which eliminates one of the biggest pain points in traditional SHG construction. For small refractors (under 4” aperture), an energy rejection filter (ERF) is not required. This reduces setup complexity and cost. For larger apertures, users can add a standard ERF or a front-mounted filter to manage heat and protect the optics.
Scientific and creative potential
Beyond its imaging performance, the SHG 700 opens doors to amateur solar spectroscopy. Users can track the dynamics of chromospheric features over time, compare images across different wavelengths, or even detect Doppler shifts in active regions.
From a creative standpoint, it allows astrophotographers to produce full-disk solar portraits in multiple wavelengths, each revealing different solar layers and processes. The detail revealed in H-alpha filaments, calcium plage, or helium loops can rival professional observatory images when conditions are good.
Outreach possibilities also expand. While live viewing isn’t possible, the workflow of capturing and assembling an SHG image can become a compelling part of solar astronomy demos, especially for high school or university audiences.
Availability and price
The MLAstro SHG 700 is available to pre-order from the official website for $880.
The MLAstro SHG 700 represents a turning point in amateur solar imaging. It simplifies a once-complex technique and packages it in a form that’s accessible, reliable, and high performing. It offers unmatched resolution and versatility for those seeking more than traditional H-alpha views and willing to trade real-time imaging for ultra-fine detail. As solar activity continues to ramp up toward Solar Maximum, now is the perfect time to explore the Sun beyond the surface. The SHG 700 doesn’t just show you the Sun, it lets you dissect its light, one angstrom at a time.
Clear skies!
