Overview of All Hole Diameters for Large Format Lens Boards (Compur, Copal & Compound)

What are lens boards?

Lens boards are used in large format photography to mount the lens along with the shutter to the camera.

Different camera systems use different lens boards, which vary in both size and shape.

We currently offer lens boards in five different versions (sorted by size):

1. 80 x 80 mm lens boards for Horseman 45FA, 45HD, VH
2. 92.5 x 94 mm lens boards for Graflex Crown & Speed Graphic
3. 96 x 99 mm lens boards for Linhof, Technika, Ebony, Tachihara, Wista, Shen Hao, Chamonix
4. 110 x 110 mm lens boards for Toyo Field 4x5 45A II CF A AR AII AX
5. 140 x 140 mm (effective 139.7 mm) lens board for Sinar & Horseman View

Depending on the size and focal length of the lens used, the lens board must also have a specific hole diameter. Lens boards are usually delivered pre-drilled by the camera manufacturer. However, if no replacement lens board is available, a custom one must be made. We supply such custom lens boards in various sizes and with different hole diameters.

The diameter of the drilled hole is generally referred to as the "Copal number." We offer the lens boards listed above with all common Copal, Compur, and Compound hole diameters.
(Note: The maximum selectable hole size is limited by the outer dimension of the respective lens board.)

Copal shutters

• Copal #0 — 34.6 mm
• Copal #1 — 41.6 mm
• Copal #3 — 65.0 mm
• Copal #3S — 64.1 mm (variant of #3 with smaller rear thread diameter; often also listed as 64.5 mm)

Noticeable: There is no "Copal #2". Nidec Copal skipped this size for large format lenses — the jump goes directly from #1 to #3. This sometimes confuses beginners but is correct.

Compur shutters (historical sizes)

• Compur #00 — 26.3 mm
• Compur #0 — 34.6 mm
• Compur #1 — 41.6 mm
• Compur #2 — 52.5 mm (there were various versions of Compur II and Compur II 5/2)
• Compur #3 — 65.0 mm

Compound shutters (historical sizes)

• Compound Dagor — 38.0 mm
• Compound #3 sleeve 7 — 63.2 mm
• Compound #4 sleeve 9 — 69.1 mm
• Compound #4 sleeve 10 — 80.0 mm
• Compound #5 sleeve 12 — 93.4 mm

Note: In some cases, the hole diameters for Copal and Compur are identical — e.g., for #0 (both 34.6 mm).

Recessed and blank variants

We also supply lens boards in the "Recessed" variant. Here the opening is set inward (usually by 12 mm or 17 mm, depending on the camera system), which allows the use of especially wide-angle lenses.

Lens boards marked as "Blank" are delivered without holes and are suitable for anyone who has an unusual lens size and wants to drill the hole themselves.

Practical tips for installation

• Anti-rotation pin: Almost all leaf shutters have a small protruding screw on the back that secures the shutter against rotation in the board. Custom-made lens boards lack the matching notch — it must either be filed in or the screw removed from the shutter.
• Off-center hole: For Linhof Technika lens boards (96 x 99 mm), the hole is often not exactly centered from the factory but slightly offset downward so that the optical axis correctly points to the film. If you drill a blank board yourself, you should plan for this offset.

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Video: How to mount a lens on a lens board

David Hancock shows in this tutorial how to correctly mount a lens with a Copal shutter on a lens board:

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