Pinhole calculator
Type the distance from the pinhole to the film: you get the hole to drill, its f-number and the angle of view — and, with the light and a film, the time to expose.
Your camera and the light
What to drill, and what to expose
- Hole diameter
- 0.315 mm
- f-number
- f/158.7
- Nearest third of a stop
- f/128 + ⅔
- Angle of view, diagonal
- 46.8°
- Angle of view, horizontal
- 39.6°
- Angle of view, vertical
- 27.0°
- Corner fall-off (darker than the centre)
- 0.5 stops
- Metered time
- 0.8 s
Worked out for a hole of 0.315 mm, f/158.7.
Choose a film to add the maker’s reciprocity correction to the metered time.
Expose for
0.8 s
One second or less needs no correction: expose as metered.
Expose for
—
Metered 0.8 s · Added +— stops
Not published
0.8 s is beyond the longest time in the maker’s table, and the table is not extended past its last point. Bracket generously, or test.
No number published
The maker states the correction in words only, so there is nothing to compute: see the rule below.
The maker’s words (not computed)
Formulas and where they come from
A
The hole
d = c · √(f · λ): f is the distance from the hole to the film and λ the wavelength of the light. Four values of c are in print:
- Petzval, 1857: c = √2 ≈ 1.414.
- Young, 1971: c = √2.44 ≈ 1.562. Applied Optics 10(12), 2763 ↗
- Rayleigh, 1891, his visual optimum: c = 1.9. Phil. Mag. 31, 87–99 ↗
- Rayleigh, 1891, the theoretical value: c = 2. Nature 44, 249 ↗
B
The picture
- f-number: N = f / d, named to the nearest third of a stop, k = round(6 · log₂ N).
- Angle of view: 2 · atan(x / 2f), for the film’s diagonal, width or height x.
- Corner fall-off: cos⁴θ, where θ is the angle from the axis to the corner of a flat film.
C
The exposure
- Metered time: t = N² / 2^EV · 100 / ISO, with the exact f-number of the hole.
- Light by condition: EV at ISO 100 from ANSI PH2.7, as listed in Wikipedia’s “Exposure value”. Where it gives a range (9–11, 5–7) the middle is used.
D
Reciprocity
The maker’s own data, worked out as on the Long exposures page: nothing at a second or less, Tm^P where the maker gives an exponent, the maker’s table read between its points, and nothing past the end of a table. Where a maker gives words only, the words are shown and nothing is computed.
The same numbers, in your pocket: Pinhole Calc for iPhone.