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Pinhole Wall & Front-Board Mount

1. Purpose

The pinhole wall is the far (scene-facing) end wall of the container — the plane that carries the camera's aperture. This report covers the wall interface: the aperture cut through the container wall and the flat wall-frame adapter that the front board bolts to. The front board itself — the interchangeable pinhole/lens mount — is the Pinhole Disc Holder; the pinhole optics are in the Pinhole Optics Report.

The former standard Ø600 interchangeable pinhole/lens plate (8× M12 on a Ø540 wall frame, with separate pinhole and lens plates) was retired. The compact Ø80-carrier disc holder now does both jobs — a pinhole board or a large-format lens board (Copal/Compur 0/1/3) — from one small mount, and focus for a lens is set at the film plane (the rear standard's depth rail), so no lens-plate focus tube is needed.

2. Wall Aperture

The far end wall is corrugated ISO container steel. A circular aperture is cut through the corrugation on the optical axis (pinhole center: X = 2,454mm on the long axis). The cut clears the front board's Ø110 scene-side taper bore with margin; it is not a precision feature — the flat adapter over it provides all the alignment datum.

3. Wall-Frame Adapter

Because corrugated steel cannot seat a machined plate, a flat steel adapter plate is welded (or bolted) over the corrugation to present a flat, machined datum face concentric with the aperture. It carries:

  • the 4× M6 tapped holes on a Ø150 circle that the Ø180 front plate bolts to (matching the disc holder — see its report),
  • a flat sealing face for the front-board gasket / O-ring, and
  • an opening larger than the Ø110 taper bore.

The adapter is the only component welded to the container; every optical-alignment reference originates from its machined face. Its bolt pattern and aperture are single-sourced from the Pinhole Disc Holder (§2/§6).

4. Front Board (the mount)

The interchangeable pinhole/lens mount is the Pinhole Disc Holder — a compact Ø180 front plate that bolts to the adapter and clamps an interchangeable Ø80 carrier (a pinhole board, or a Copal/Compur lens board) with a retaining ring and four thumb screws. Changeover between pinhole and lens is a seconds-long carrier swap; see that report for the mechanism, drawings, tolerances and BOM.

5. Sealing & Light Integrity

Two joints seal the wall:

  • Adapter → container wall: continuous weld (or a bead of sealant under a bolted adapter) around the aperture — no light path around the adapter.
  • Front board → adapter: a thin gasket (or an O-ring in the adapter face) compressed by the 4× M6 mount bolts, backed by a perimeter light-trap step, so any light passing the gasket must navigate a labyrinth before reaching the interior.

The carrier itself (pinhole or lens) is the only intended opening; its seal against the front plate is covered in the disc-holder report §5.

6. See Also

7. Source References

  1. Rayleigh Criterion for Pinhole Cameras — optimal aperture formula d = 1.9√(fλ).
  2. Intrepid Camera — Large-Format Lens Explorer — Copal/Compur lens-board hole diameters for the carrier.
  3. McMaster-Carr — mount bolts, gasket / O-ring cord, weld consumables.