How to Use the Solar Pinhole Camera

Aim a virtual pinhole can, pick a place and a number of days, and see the Sun trails it would burn onto the paper.

Sun safety: never look at the Sun directly, through the pinhole, or through a camera viewfinder, binoculars or a telescope. A solargraph can is safe because nobody looks through it: you mount it, walk away, and open it later in dim light. Aim it with a compass or by its shadow, not by eye. Any lens pointed at the Sun needs a certified solar filter over the front, and eclipse glasses are for bare eyes only, never behind optics. Supervise children at all times.

What this tool answers

Where will the Sun's trails land on the paper if I point my can this way, at this place, for this many days? It models an upright can with a pinhole in the middle of its side wall and photographic paper curled around the inside wall, then draws the Sun's path over your exposure as a Simulated paper. For the craft of building, sealing and scanning a real can, read Solargraphy.

What you see on the screen

Under the amber Sun safety note, a wide screen shows the settings on the left in six sections: Container, Pinhole, Paper, 3D preview, Location and Exposure. The right side holds a 3D view of the can under the sky, then two dials, Bore azimuth and Bore altitude, then two cards side by side: Simulated paper and Optics. Real solargraphs follow under Real paper results. On a phone the 3D view, dials and cards come first, and the settings follow as sections you tap to open or close.

Step by step

Open the Solar Pinhole Camera.
Under Container, pick your can. It fills Focal length (f) and Inner radius in mm. Replace them with your own caliper measurements.
Under Pinhole, pick a needle or pin preset (default Sewing needle #10 (~0.48 mm)), or type Diameter (∂) and Wall (w) in mm.
Under Paper, pick your paper. Leave Mirror (emulsion / glossy side) on for the Ilford presets.
Under Location, pick a Guyana town, press the map pin button to use your device's location, or type Latitude and Longitude.
Under Exposure, set Start date and drag Exposure days (1 to 365, default 7).
Drag the Bore azimuth compass to the direction the pinhole faces (0° north, 90° east by default, 180° south, 270° west).
Drag the Bore altitude dial to tilt the can upward (0° to 90°, default 0°). A real can tilts with a cork or wedge under its back.
Watch Simulated paper and change the aim until the trails sit well on the paper.
Take a screenshot of your settings for the build.

Optional controls:

Step (min): how often the Sun is sampled (default 10).
Horizon cutoff (°): hides the Sun below that altitude, a rough stand-in for trees or buildings (default 0).
Atmospheric refraction: on by default.
Cloudy weather (broken / faded trails): adds gaps and fades, with a Typical cloud cover slider from 25% to 95% (default 55%).
Negative (paper), Sky background and Can model: change how the preview and the 3D can look, not the result.

The real simulator at Georgetown in June: facing east at 0° tilt only the low morning Sun lands on the paper; turned north and tilted 45° up, nearly the whole day does.

How to read the results

Simulated paper shows the whole sheet, sky at the top and ground below a faint white horizon line. Each day draws one Sun trail, brightest where the Sun shines straight into the hole. The caption counts how many Sun samples land on the paper. If none do, an amber note says "No sun samples land on the paper with this aim, site, and exposure window" and suggests a new aim, a lower horizon cutoff or more days.

The simulator's own Sun track for Georgetown or Lethem: aim and tilt the can, pick a start date and a number of days, and watch the paper.

In the 3D view, the cyan dashed outline (paper FOV) is the sky the paper sees, and the yellow line (pinhole / bore) is the hole's aim. Trail colours run from Start to Mid to End of the exposure. A pale yellow ball marks the Sun right now, if it is up at the chosen place. An amber dashed ring (θ_vig) appears when a thick wall cuts off light from the sides.

The Optics card matches the calculator's, including Capture width and Capture height (±77° and ±44° by default), and turns amber above 1.5 or below 0.6 times the optimal hole. The Pinhole Optics Calculator guide explains each readout.

An east-facing solargraph from Guyana: steep Sun arcs, with gaps on cloudy days. Credit: Samir Mohammed / AstroPhotosGY.

Using it from Guyana

At Georgetown the noon Sun passes overhead about 6 April and 4 September (about 28 March and 13 September at Lethem). From 7 April to 4 September it is north of overhead, reaching 73.4° up at the June solstice; the rest of the year it is south, down to 59.8° at the December solstice. This changes how you aim:

The noon Sun's height through the year from Georgetown and Lethem, north or south of overhead.

South at 0° tilt gives an empty paper at Georgetown from April to early September, because the Sun stays on the north side.
East or west at 0° tilt records only the low part of the day. In early April, when the Sun rises almost due east, the trails stop at about 43° altitude, roughly the first or last three hours.
A 45° tilt facing north in June, or facing south in December, keeps nearly the whole day on the paper.

It is June in Georgetown and your can faces due south at 0° tilt. What will the paper show?

Long, high arcs across the middle
Short arcs near the top
Almost nothing: the Sun stays on the north side (the right answer)
Trails only on cloudy days

From 7 April to 4 September the noon Sun is north of overhead at Georgetown, so a can facing south at 0° tilt sees almost none of its path.

Take the aim the Solargraph Install Planner suggests for your site and dates, dial it in here, and check every month you plan to expose. Sun Path Today, Hour by Hour lists the Sun's altitude and direction at each hour of today. For a coastal exposure in the wet seasons (mid-April to end of July, mid-November to end of January), turn on Cloudy weather to see broken trails.

The simulator shows no clock times. Each simulated day starts at local midnight from your longitude, within about 8 minutes of Guyana time (UTC-4) at Georgetown.

What it does not do

It has no export, save or share link, and reloading the page resets every setting.
It models only an upright can with a side pinhole, not a flat-back box.
Clouds are a repeatable random model, not a forecast. The horizon is one flat cutoff, not your skyline, and Photo sky (CC0 HDRI) is a generic sky.
It does not suggest an aim or give exposure times. Use the planner above, or Pinhole Daytime Exposure for a full-sun exposure estimate.
It cannot show light leaks or damp paper, which can ruin a real solargraph whatever the aim. Load the paper dry and seal the can well.

Common mistakes

Aiming south at 0° tilt between April and early September in Guyana. The Sun stays north and the paper stays empty.
Leaving the tilt at 0° and wondering why midday is missing. Straight ahead, the paper reaches only about 44° up.
Trusting preset sizes instead of measuring Inner radius and Focal length (f).
Turning Mirror off for glossy Ilford paper, which flips the preview left to right.

Your can faces east at 0° tilt. Why are the midday hours missing from the trails?

The pinhole is too small
Straight ahead, the paper reaches only about 44° up, and the midday Sun is higher (the right answer)
The Sun is weaker at midday
The Mirror setting hides them

With the default can and 5×7" paper the sheet covers about ±44° up and down from the bore, so a level can misses the high midday Sun; tilt it up to catch more of the day.

Size the hole with the Pinhole Optics Calculator.
Learn why the optimal hole is 1.9 × √(λ × f) in Pinhole Optics.
Build, seal and scan a real can with Solargraphy.

How to Use the Solar Pinhole Camera