Flat vs Curved Film Plane in 6×17 Pinhole Photography

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A Technical Comparison

There’s something beautifully simple about a pinhole camera — just light passing through a tiny hole onto film.

But when that film sits in a 6×17 camera, one important question appears:

Should the film be flat… or curved?

Recently I took two 6×17 pinhole cameras out side by side:

The focal lengths are very close, so the real comparison here is geometry — how the shape of the film affects the way light is recorded.

Here’s what I found.


1. Why Film Curvature Matters in a Pinhole Camera

A pinhole does not naturally project an image onto a flat surface.

The sharpest focus actually falls along a curved surface, part of a sphere centred on the pinhole.

So:

  • A flat film plane forces a curved projection onto a flat sheet.

  • A curved film plane follows the natural geometry of the projection.

This difference becomes more noticeable in wide formats like 6×17, where the edges are far from the centre.


2. Edge Sharpness

With the flat film plane (Mia 6×17 3P):

  • The centre of the frame is at the stated focal length (66mm).

  • The edges are physically further away from the pinhole.

  • That increases the effective focal distance toward the edges.

  • Result: gradual softness toward the extremes.

With the curved film plane (RealitySoSubtle 6×17):

  • The distance from pinhole to film stays more consistent.

  • Edge sharpness is more evenly maintained.

  • The frame feels optically balanced.

This isn’t dramatic, but it is visible when comparing negatives carefully.



Curved Field of view VS Flat Field of View
RealitySoSubtle 141°
Mia 104°

3. Light Falloff and Illumination

Light hitting the edges of a flat film plane arrives at a steeper angle than light hitting the centre.

That causes:

  • Stronger edge darkening

  • More noticeable natural vignetting

With curved film:

  • The angle difference is reduced.

  • Illumination across the frame is more even.

  • Sky gradients appear smoother.

On wide landscapes, especially with large areas of sky, this becomes noticeable.




4. Stretching and Rendering

Flat film tends to produce:

  • Slight stretching toward the edges

  • A more dramatic panoramic feel

  • Increased visual tension at the extremes

Curved film tends to feel:

  • More immersive

  • Less exaggerated at the edges

  • More “wrapped” around the viewer

Neither is better — they simply interpret space differently.

5. Horizon Behaviour When Tilting

One of the most interesting differences appears when tilting the camera upward or downward.

With a curved film plane:

  • The projection follows the curvature of the film.

  • Horizons and straight lines can subtly bow to match the curve.

With a flat film plane:

  • Straight lines remain straighter.

  • Distortion appears more like stretch rather than bend.

This is pure geometry at work — no lens involved.





6. Loading and Practicality

Beyond the optical differences, there’s a practical side.

Flat film plane:

  • Easier to load.

  • Simpler construction.

  • More straightforward in the field.

Curved film plane:

  • More precise engineering.

  • Slightly more careful loading.

  • Designed specifically to match projection geometry.

In day-to-day use, flat is simpler. Curved is more optically intentional.

7. The Real Question

In 6×17 pinhole photography, we are already working with extreme width.

So the question becomes:

Do we prioritise simplicity and practicality?
Or do we attempt to match the natural geometry of light itself?

Both cameras produced beautiful negatives. The differences are subtle, but they are there — in edge behaviour, falloff, rendering and horizon shape.

And in the end, that’s what makes this comparison fascinating.

Two cameras.
Same format.
Same light.
Different interpretation.


Watch the video



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