SOL'EX: A 650 GRAM 3D PRINTED BOX THAT PHOTOGRAPHS THE SUN IN A SINGLE WAVELENGTH
A 650 gram printed box that resolves the Sun's hydrogen alpha line finer than the 7 metre observatory instrument at Meudon.
by Christian Buil
ScienceOpen-hardware
- 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
- 3D printer + filament — printable parts — files are in the repo
Partner
COMPAREE VERDICT
Sol'Ex is a spectroheliograph: it photographs the Sun in one narrow wavelength at a time, revealing the chromosphere, prominences, and even a Doppler map of the solar rotation. The classical instrument that does this at the Meudon observatory occupies an entire building; Sol'Ex does it in 650 grams behind an amateur telescope, with finer resolution on the hydrogen alpha line. The printed parts are published, but the optical heart of the project — the grating, prism and lens set — is a 409 euro purchase from Shelyak, and you need a telescope, a proper solar filter, and a camera that can scan the disk. This is not a beginner project: you are pointing a telescope at the Sun, which causes instant permanent eye damage if you skip the filtering step, and the learning curve assumes you already know your way around amateur astronomy hardware. The single thing most likely to go wrong is buying an incompatible camera or telescope without checking the focal length and sensor requirements first. If you have the telescope already and the spectroscopy fascinates you, this is the open route to chromospheric imaging. If you are starting from zero, the cost and risk are both higher than the 409 euro optics suggest.
IN THE REPO
NOT IN THE REPO
- —STL files for the printed enclosure are in the repository under CC BY-SA 4.0.
- —The optical set (grating, prism, lenses) is not open and must be 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.
- —Licence permits commercial use.
- —No firmware — this is an optical instrument, the scanning and reconstruction happen in separate acquisition software.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
Partner · KickstarterHeyGears G1: 10M+ colors and transparent parts in one print, plus UV printing on flat objects. Figures, parts and labels — no painting.
Gallery
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 optics assume a specific focal length and sensor size — buying the Shelyak set before checking this is the most expensive mistake)
- 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 repository STL files (PLA or PETG, ordinary FDM settings)
- 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.
- Official site, design by Christian Buil astrosurf.com
- Optical set: grating, prism and lenses shelyak.com
KNOWN ISSUES
- Buying the optics before confirming your telescope focal length and camera sensor match the published requirements — this is a 409 euro mistake.
- Attempting solar observation without a proper dedicated solar filter causes instant permanent eye damage; ordinary ND filters and exposed film do not work and will blind you.
- Assuming you can substitute the Shelyak grating and prism with similar-looking parts — the resolving power depends on the exact optical design and you cannot replicate it without the specifications.
- Starting this project without prior amateur astronomy experience — the documentation assumes you already know how to safely handle solar imaging hardware.
- 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 the learning curve on the acquisition software — reconstructing a solar image from spectral scans is not automatic and takes practice.
Can I use this without a telescope?
No. Sol'Ex mounts behind a telescope and relies on the telescope's optics to form the initial solar image. The documentation specifies the focal length and aperture you need.
Is the Shelyak optics set the only option?
It is the only published source for the exact grating, prism and lens combination that gives the design its resolving power. You cannot substitute it with generic optics without recalculating the entire optical path.
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?
Absolutely not. The telescope must have a dedicated solar filter installed before pointing it anywhere near the Sun. Looking through it directly or with an improvised filter causes instant permanent blindness.
Is this actually better than the Meudon observatory instrument?
On hydrogen alpha resolution, yes: 0.16 angstrom versus 0.25 angstrom. The Meudon instrument is from an earlier era and was built for different research priorities. That does not mean this is easier to use — the observatory has trained operators and does not rely on a single person following a safety checklist.
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Discussion1
FROM THE COMPAREE TEAM
The resolving power of 40,000 means you can see Doppler shifts from the Sun rotating — one half redshifted, the other blue. What would you image first: a prominence erupting off the limb, or the velocity map of a sunspot crossing the disk?
Christian Buil
Christian Buil is a French amateur astronomer known for designing accessible spectroscopy instruments. Sol'Ex applies professional-grade spectroheliograph principles to equipment an amateur can mount and operate, bringing chromospheric solar imaging within reach of the backyard observatory. The design prioritises resolution and published documentation over cost reduction.
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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.
CompareeTEAM15d ago
Practical notes from our verification: the repository at github.com/jscheidtmann/solex is a build report, not the official design source — the complete documentation, optical specifications, and assembly instructions are at astrosurf.com/solex by Christian Buil. The 409 euro Shelyak optics are the only published source for the grating and prism set; there is no open substitute. We did not verify the Shelyak link because no URL was provided, but the part number and price (409.20 euros including VAT) are stated in the payload. The repository licence is CC BY-SA 4.0 and covers the STL files; the Shelyak optics are a commercial product and not covered by that licence. The single biggest risk is not mechanical — it is pointing a telescope at the Sun without the correct filter, which the documentation warns about explicitly and which we repeated in the safety section because it is not negotiable.