How do I size the pinhole for a large-format paper pinhole camera?
Asked 5/20/2014
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I want to build a large-format pinhole camera using photographic paper instead of film. Most guides I’ve found focus on smaller formats like 4x5. When scaling up to a larger camera, what changes in the pinhole design? Specifically, how should I choose the pinhole diameter relative to the distance from the pinhole to the paper to get the sharpest results?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
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The thing that changes with pinhole camera size is the best pinhole diameter to use. The optimal pinhole diameter is such that your pinhole-to-paper distance is the "Fresnel length" (please google for definition) of the pinhole at some representative wavelength of your filter bandpass. If you don't use a filter then you can guesstimate the sensitivity of the paper as a function of wavelength, consider your illumination spectrum (approximately solar spectrum) and go for somewhere in the middle.
Using the optimal pinhole diameter gets you the best compromise between diffraction blur (which increases with decreasing pinhole diameter) and the geometric "circle of confusion" (decreasing with pinhole diameter). Ansel Adams' book "The Camera" describes this in photographic terms, and college optics books describe this in physics terms.
3rd party edit: What this means in practical terms is: to get an 8×10” camera from a 4×5” design, scale all dimensions by a factor 2, except the pinhole diameter, which should be scaled by a factor √2̅ ≈ 1.414.
Originally by user33967. Source · Licensed CC BY-SA 4.0
user33967
11y ago
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Generated from our catalog & community — verify before relying on it.
For a larger pinhole camera, the main design factor that changes is the pinhole diameter relative to the pinhole-to-paper distance.
There’s an optimal pinhole size that gives the best balance between two types of blur:
- diffraction blur, which gets worse if the hole is too small
- geometric blur, which gets worse if the hole is too large
The goal is to choose a pinhole diameter so the pinhole-to-paper distance is appropriate for that hole size. In physics terms, this is tied to the Fresnel length for a representative wavelength of light. If you’re not using a filter, a practical approach is to estimate based on the wavelengths your photographic paper is most sensitive to and the light source spectrum, then choose a middle wavelength as your reference.
So when scaling up from 4x5 to larger formats, the camera can be larger, but you should recalculate the pinhole diameter for the new image distance rather than simply enlarging the whole design. That will give you the sharpest compromise possible for the format.
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