SOL'EX: A 500 GRAM 3D PRINTED BOX THAT PHOTOGRAPHS THE SUN IN A SINGLE WAVELENGTH
A 500 gram 3D printed box behind a small telescope that images the Sun in a single wavelength, fine enough to resolve 0.16 angstrom on the hydrogen alpha line.
by Christian Buil and Valérie Desnoux
ScienceOpen-hardware
Built with3D printing
- difficulty
- ●●●●●
- time
- a weekend-plus
- license
- CC BY-SA 4.0
- repo
- repo ACTIVE1 stars
●●●●● · a weekend-plus · CC BY-SA 4.0 · 1 stars · repo ACTIVE
WHAT YOU’LL NEED
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COMPAREE VERDICT
Sol'Ex is a spectroheliograph: it photographs the Sun in one narrow wavelength at a time, revealing the chromosphere, prominences, and even Doppler maps of moving gas. Instruments like this used to live mainly in professional observatories; Sol'Ex weighs about 500 grams and mounts behind an ordinary refractor or even a telephoto lens, with a calculated resolution of about 0.16 angstrom on the hydrogen alpha line. The printed parts are published, but the optical heart of the project, the lens, grating and slit set, is a 409 euro purchase from Shelyak (equivalent lenses and grating are also sold by Thorlabs), and you need a telescope or long lens, an attenuating filter in front of it, a planetary camera and focusers. The authors say the kit can be assembled in a few hours and that a newcomer to spectroscopy can succeed, but the alignment and scanning take practice. The non-negotiable rule is solar safety: the project makes an attenuating filter mandatory so the Sun's focused heat does not melt the plastic parts, and you must never look through the telescope at the Sun. If spectroscopy fascinates you, this is the open route to chromospheric imaging.
IN THE REPO
GOOD TO KNOW
- —The printable body parts come from the Sol'Ex authors (linked from astrosurf.com/solex); this repository is a CC BY-SA 4.0 build diary that adds one extra centering piece.
- —The optical set (lenses, diffraction grating, slit) is not open and is bought from Shelyak for 409.20 euros including VAT.
- —You supply your own telescope, solar filter, and camera — the project assumes you already have them or know which to buy.
- —The repository is a build report by Jens Scheidtmann; the original design and full documentation live at astrosurf.com/solex by Christian Buil.
- —The CC BY-SA 4.0 licence covers this build diary only; check the official Sol'Ex files for the design's own terms before any commercial use.
- —No firmware — this is an optical instrument, the scanning and reconstruction happen in separate acquisition software.
Parts to buy
3 itemsFrom our check of the build. Exact quantities and part numbers are in the creator’s BOM.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
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Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Read the full documentation at astrosurf.com/solex before ordering anything (The repository is a build report; the actual design manual is on Christian Buil's site and covers telescope compatibility, focal length requirements, and the acquisition procedure)
- 2.Confirm your telescope and camera are compatible with the published specifications(The documentation recommends a telescope or lens with 200 to 1200 mm focal length, around f/5.6 to f/9, plus a planetary CMOS camera.)
- 3.Order the Shelyak optical set(409.20 euros including VAT; this is the part you cannot print or substitute)
- 4.Print the enclosure parts from the official Sol'Ex files (Black PETG is recommended; the filament must be black so it blocks visible and near-infrared stray light.)
- 5.Assemble following the astrosurf documentation, not the repository alone (The repository is one builder's report; the official assembly sequence is on the main site)
Resources
Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.
KNOWN ISSUES
- Not checking your telescope first: the documentation recommends a focal length between 200 and 1200 mm and apertures around f/5.6 to f/9; outside that range results suffer.
- Skipping the attenuating filter. The project makes a filter in front of the telescope mandatory (a photographic neutral density filter such as the HOYA PROND, or a Herschel wedge, as documented), otherwise the concentrated sunlight melts the printed parts. Check it with the documented test: you should be able to hold your palm at the focus for 15 to 20 seconds. Never look through the telescope at the Sun.
- Substituting random similar-looking optics: the design needs an 80 mm and a 125 mm achromatic doublet and a 2400 lines per millimetre grating. Use the Shelyak kit or the exact Thorlabs equivalents listed in the official documentation.
- Expecting instant results: the documentation guides you step by step, but aligning the slit, focusing and orienting the camera, and reading a solar spectrum all take practice on the first sessions.
- Using the repository as the sole build guide when the complete documentation is on astrosurf.com/solex — the repository is one builder's report, not the official manual.
- Underestimating acquisition: the free INTI software reconstructs the image automatically, but recording a clean scan (focus, orientation, drift speed, exposure) takes practice.
Can I use this without a telescope?
No. Sol'Ex mounts behind a refractor, a finderscope or a telephoto lens, which forms the solar image on its slit. The documentation recommends a focal length of 200 to 1200 mm.
Is the Shelyak optics set the only option?
No. Shelyak sells the official optical kit (lenses, 2400 lines per millimetre grating and slit), but the Sol'Ex documentation also lists equivalent parts from Thorlabs with comparable performance: AC254-080-A collimator lens, AC254-125-A camera lens and GH25-24V grating.
What does 'resolving power of 40,000' mean?
It means the instrument can distinguish wavelengths that differ by one part in 40,000. On the hydrogen alpha line at 656.3 nanometres, that corresponds to about 0.16 angstrom resolution, fine enough to see Doppler shifts from the Sun's rotation.
Can I look through this at the Sun directly?
No. Sol'Ex is an imaging instrument: a camera records the spectrum, you never look through it. Never look at the Sun through the telescope. The project also requires an attenuating filter in front of the telescope (a neutral density filter or a Herschel wedge, as documented) so the focused sunlight does not melt the printed parts.
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Discussion1
FROM THE COMPAREE TEAM
The official Sol'Ex site shows Doppler images of the chromosphere, where colour reveals gas moving towards or away from you. What would you image first: a prominence erupting off the limb, or the motion around a sunspot?
Christian Buil and Valérie Desnoux
Christian Buil and Valérie Desnoux are French amateur astronomers behind Sol'Ex: Buil designed the instrument and Desnoux wrote the INTI processing software. Sol'Ex brings the spectroheliograph, long mainly a professional observatory tool, to amateurs at an affordable price, with printable parts, an optical kit and extensive documentation.
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DISCLAIMER
- Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM2mo agoedited
Practical notes from our verification: the repository at github.com/jscheidtmann/solex is Jens Scheidtmann's build diary, not the design source — it contains photos and one helper STL. The official Sol'Ex project by Christian Buil and Valérie Desnoux is documented at astrosurf.com/solex, and the printable STL files are in the Vdesnoux/Sol-ex repository. The optics — lenses, a 2400 lines per millimetre diffraction grating and the slit — come as a kit distributed for the Sol'Ex project through Shelyak. The diary's CC BY-SA 4.0 licence covers the diary itself, not the optics or the official design. There is also a mostly French mailing list on groups.io where new developments are posted. The single biggest risk is not mechanical: never point the telescope at the Sun without a proper solar filter. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.