Solar Filter for Unistellar Odyssey (Baader AstroSolar OD 5.0)

I shot the partial solar eclipse of August 12, 2026 through this filter on my Unistellar Odyssey. The gallery has both a single frame straight from the telescope (orange = low Sun plus the camera's warm rendering) and a stacked, color-calibrated 16-bit master — sunspot groups clearly visible. Bench-fitted on my Odyssey with the printed gauges: the cell slides on by hand with clear resistance, seats on the tube's front rim, and stays put — no wobble, and it doesn't fall off.

⚠ Read this first — solar safety

A full-aperture solar filter that comes off while the telescope is pointed at the Sun destroys the sensor in a fraction of a second. The Odyssey is camera-only, so no eyes are at risk — but on an eyepiece instrument the same failure blinds you. This is a DIY device; you build and use it at your own risk.

- Print in ASA or ABS only — never PLA (see Printing below).

- Before every use, hold the film up against a bright lamp: any pinhole, micro-tear or scratch means the film is discarded and you do not observe.

- Tug-test the cell on the tube every time. Fit the filter before pointing at the Sun, remove it only after slewing away, and never leave the instrument pointed at the Sun unattended.

What it is

A filter cell and retaining ring that clamp a Ø120 mm disc of Baader AstroSolar® Safety Film OD 5.0 flat between two annular faces over a 6 mm band — the Baader-endorsed method. The film is never stretched, glued or tensioned: it lies slack between the faces, and the wrinkles you see in the photos are normal and optically harmless.

Design points:

- Rim-registered film plane. An internal shoulder (45° funnel ending in a 1.5 mm flat ledge) lands on the tube's front rim , so the rim — not a guessed insertion depth — sets the film position. The film sits ~3.2 mm in front of the rim; total overhang past the rim is only ~7.7 mm.

- Ø108 mm clear aperture over the Odyssey's Ø85 mm entrance beam: 11.5 mm of radial margin while the cell centers on the tube to better than 1 mm. No vignetting possible.

- Lug relief slot. The tube's lug gets a 3.6 mm-wide, 5 mm-deep slot (measured off the source mesh). The slot stops below the rim seal, so it can never become a light path into the tube.

- A 26 mm skirt (2.2 mm wall, 45° lead-in chamfer) grips the tube; default bore Ø114.22 mm , bracketed by three printable fit gauges.

Film sourcing

Use AstroSolar® Safety Film OD 5.0 from Baader Planetarium GmbH — the 20 × 29 cm sheet (article no. 2459281). One Ø120 mm disc comes out of each half sheet, so a single sheet builds this filter twice .

Do not substitute AstroSolar Photo Film OD 3.8 — that is photographic film and is never safe for visual use. OD 5.0 only.

Printing

- ASA mandatory (or ABS). No PLA: the part sits in full sun, PLA creeps at 55–60 °C, and a sagging filter falls off — see the safety block above.

- No supports, no raft. Every part is self-supporting in the 3MF orientation (skirt down for the cell, clamp face down for the ring); 45° rules are respected by design.

- 0.20 mm layers, 4 perimeters, 30–40 % infill. Enable ironing on top surfaces: the cell's top face is the film seat and must be flat.

- Print plate 1 (the three fit gauges) first and alone (~25 min). Confirm the fit on your tube, adjust BORE_D in the script if needed, then print plate 2 (cell + ring + template).

- Printed on a QIDI X-Max 4 in black ASA. Masses: cell ~53 g, ring ~18 g, template ~3 g.

Hardware

- 6 × M3 heat-set inserts, Ø4.2 × 6 mm (the standard short M3 insert)

- 6 × M3×8 cap-head screws

- Optional: 3 × M4×16 nylon thumb screws for the radial lock bosses. On my unit the fit is snug enough that I never installed them — the bosses are printed with Ø3.3 mm pilot holes, so drilling/threading them later is cheap insurance if your fit turns out looser.

- Optional, recommended: a 1 mm soft foam ring (Ø120 outer / Ø112 inner) glued under the retaining ring — softer, more even clamping, and it keeps the plate-side texture off the film.

Getting the fit right

The three fit gauges bracket the bore: A = Ø114.22 (8 mm tall), B = Ø114.72 (11 mm), C = Ø115.22 (14 mm) — told apart by height, and all carry the lug slot. Try A, then B, then C, lug in the slot. Target: slides on by hand with clear resistance and does not fall off under its own weight.

If your tube wants B or C, edit the single BORE_D constant in solar_filter_odyssey.py and re-export. The source is fully parametric CadQuery and runs its own geometry self-tests on every build: self-supporting angles, fully buried inserts, clamp-band width, film/screw non-interference, aperture margin, and a functional check of the lug slot.

Assembly

- Gauges first — confirm the bore as above.

- Melt the six M3 inserts into the cell's top face; keep them square.

- Cut the film disc using film_template : lay the film flat and untensioned , trace with a fine felt pen, cut with scissors. Handle it by the edges, never fold it.

- Film on the seat → (foam ring) → retaining ring → six M3×8 finger-tight, in a cross pattern . The film must stay slightly slack — wrinkles are normal.

- Push the cell onto the tube, lug in the slot, until it seats on the rim. Tug-test.

The assembly guide PDF in the files has the technical drawing and illustrated step-by-step.

Before every use — non-negotiable

- Inspect the film against a bright lamp: pinhole, micro-tear or scratch → discard the film, do not observe.

- Check the six M3 screws and tug on the cell by hand.