What this pinhole camera calculator does
This calculator helps you design and expose a pinhole camera quickly. Enter your camera depth (focal length), and it estimates:
- Optimal pinhole diameter based on diffraction vs. geometric blur balance
- Effective f-number of your pinhole setup
- Exposure time adjusted from a metered exposure
- A simple reciprocity correction estimate for long exposures
- Horizontal, vertical, and diagonal field of view
The core formula
A common starting point for pinhole diameter is:
d = 1.9 × √(f × λ)
where d is pinhole diameter, f is focal length, and λ is wavelength of light (in the same units as focal length). For practical camera work, using millimeters for focal length and converting wavelength from nanometers to millimeters works well.
Why this matters
If the hole is too small, diffraction softens the image. If it is too large, geometric blur increases. The formula targets the sweet spot for overall sharpness.
How to choose focal length
In pinhole photography, focal length is essentially the distance from the hole to the image plane. Shorter depths give wider views; longer depths narrow the view.
- Wide look: 25–40 mm
- Normal look: 45–65 mm
- Narrow view: 80 mm and up
You can experiment by sliding paper or film farther from the pinhole in a test box and comparing composition and edge falloff.
Exposure and reciprocity
Pinhole apertures are tiny, often around f/130 to f/300. That means exposures can jump from fractions of a second (at f/16 on a normal camera) to many seconds or minutes.
The calculator first scales exposure using:
New time = Metered time × (Pinhole f-number / Metered f-number)²
Then it applies a basic reciprocity correction estimate. Real film stocks differ, so treat this as a planning value and bracket your shots when possible.
Practical bracketing tip
- Take one shot at the calculated corrected time
- Take one at half that time
- Take one at double that time
Build tips for cleaner pinholes
- Use thin metal (e.g., beverage can aluminum or brass shim stock).
- Create a tiny dimple first, then polish gently with fine abrasive.
- Inspect with a loupe for circularity and burrs.
- Paint inner camera surfaces matte black to reduce flare.
- Keep the film/sensor plane flat and square relative to the pinhole plate.
Example workflow
Suppose your camera depth is 50 mm, wavelength is 550 nm, and your handheld meter reads 1/8 second at f/16. The calculator might return a pinhole near 0.315 mm and an effective aperture near f/159. Your uncorrected pinhole exposure will be much longer than 1/8 second, and the corrected value can extend further due to reciprocity.
This gets you close in the field without doing mental math while the light changes.
Frequently asked questions
Is this exact for every camera?
No. It is an excellent engineering estimate. Material thickness, hole quality, and film behavior all influence results.
Should I always use 550 nm?
It’s a strong default. You can experiment (e.g., 500–600 nm) for different assumptions, especially with filters or monochrome work.
Do digital sensors need reciprocity correction?
Usually much less than film, but long exposure noise and hot pixels become the practical concern. For digital pinhole shooting, start with uncorrected time and test.