Solargraph Photography: Ultra-Long Exposure Pinhole Images That Trace the Sun's Path Across Months and Seasons

Solargraphy is one of the most remarkable and accessible techniques in all of photography: a simple pinhole camera made from a drinks can, loaded with a single sheet of photographic paper, is sealed and mounted in a fixed position pointing south (in the Northern Hemisphere) or north (in the Southern Hemisphere). It is left in place for weeks, months, or even an entire year, continuously exposing the photographic paper to the scene before it. The result, when the paper is removed and scanned (without conventional chemical development), is a solargraph — an image that records the arc of the sun's path across the sky as luminous curved streaks, one for each day of operation, overlaid on a ghostly long-exposure rendering of the landscape below. Clouds interrupt individual sun trails, so overcast days leave gaps, and the pattern of complete and incomplete trails becomes a visual record of the weather over the entire exposure period.

Solargraphy is extraordinary for several reasons. It requires no electricity, no batteries, no lens, no shutter mechanism, no digital technology, and no chemical processing — just a tin can, a sheet of photographic paper, and time. The exposure times — measured in weeks and months rather than fractions of a second — are the longest in any photographic practice. The images produced are simultaneously astronomical observations (recording the sun's daily arc and its seasonal shift across the sky), weather records (the gap pattern encodes local cloud cover), and landscape photographs (the accumulated exposure records everything stationary in the scene with surprising detail). And the aesthetic — luminous sun trails arcing across deep blue or purple skies above ghost-pale landscapes — is unlike anything achievable by any other photographic method.

How Solargraphy Works: The Photochemistry

A solargraph camera uses no lens — just a pinhole pierced in the wall of the can. The pinhole projects an inverted image of the scene (including the sky and sun) onto the photographic paper lining the inside of the can opposite the pinhole. The image formation is identical to every other pinhole camera — rectilinear light projection through a small aperture — but the exposure time is astronomically long. The sun, being by far the brightest object in the scene, burns a bright trail onto the paper as it moves across the sky during the day. Over weeks of exposure, the cumulative sunlight "prints" the sun's daily arc onto the paper through direct photochemical darkening of the silver halide emulsion — no developer is needed.

The key insight is that photographic paper is a "printing-out" material — silver halide crystals in the emulsion darken when exposed to sufficient light without chemical development. This is the same principle used in nineteenth-century printing-out papers (salted paper, albumen prints, POP): light alone reduces the silver compounds to metallic silver, producing a visible image. The effect is much slower than development-based processes, which is why solargraphy requires weeks or months of exposure — but the sun's extreme brightness makes it possible. The landscape below the sun is also recorded, though at much lower contrast, as the cumulative illumination over weeks gradually differentiates between lighter and darker features in the scene.

Building a Solargraph Camera: Step by Step

Materials: an aluminium drinks can (330ml or 500ml), a sheet of black-and-white photographic paper (any type — RC or fibre, matte or gloss — will work), a sewing needle or fine pin, matte black tape (electrical tape or gaffer tape), and scissors. Remove the top of the can with a can opener, leaving a clean-edged cylinder. Some practitioners prefer to cut the can in half lengthwise (for a wider field of view) or use a larger container like a paint tin (for bigger images). Clean the inside of the can thoroughly to remove any residues.

Make the pinhole: pierce the can wall approximately halfway up, on the side opposite from where the paper will be. Use a fine sewing needle or pin — push it through from the outside, creating a clean, round hole approximately 0.2–0.3mm in diameter. The smaller the pinhole, the sharper the sun trails will be (but the dimmer the overall image). A standard sewing needle produces an adequate pinhole for most solargraphy purposes; perfectionists can use a drill bit or specialised pinhole tool for more precise results.

Load the paper: in a darkroom or under a safelight, cut a piece of photographic paper to fit the curved inner wall of the can, opposite the pinhole. The emulsion (shiny) side must face inward toward the pinhole. Curl the paper gently and insert it into the can, pressing it against the back and sides so it follows the can's curvature. The curved paper means the image is projected onto a cylindrical surface, which creates a natural wide-angle effect — typically 120–160 degrees of horizontal coverage depending on how much of the can's interior is covered by paper.

Seal the camera: replace the top of the can and seal every joint, edge, and potential light leak with matte black tape. The camera must be completely light-tight except for the pinhole. Cover the pinhole itself with a small piece of tape until you're ready to begin the exposure. Double-check all seals — any stray light entering through a gap will fog the paper and ruin the image.

Mounting and Positioning

Position the camera with the pinhole facing south (in the Northern Hemisphere) or north (in the Southern Hemisphere) to capture the sun's arc across the sky. Tilt the camera upward slightly — approximately 30–45 degrees above horizontal — so the top of the sun's highest arc (at the summer solstice) is captured in the upper portion of the paper, and the lowest arc (at the winter solstice) appears in the lower portion. If you want to include landscape in the lower part of the image, angle the camera to include some horizon.

Mount the camera securely — it must remain completely stationary for the entire exposure period (weeks to months). Cable ties, hose clamps, or strong waterproof tape can secure the can to a fence post, railing, pole, or branch. The mount must survive wind, rain, and whatever weather your location experiences. Some practitioners enclose the can in a clear plastic bag or secondary container for additional weather protection, though the can itself is already reasonably weatherproof if properly sealed.

Once the camera is securely mounted and aimed, remove the tape covering the pinhole to begin the exposure. The exposure now runs continuously, 24 hours a day, for the duration of your chosen exposure period. The sun burns trails during the day; nighttime and cloudy periods don't contribute enough light to materially affect the exposure (though the moon can sometimes leave faint traces during multi-month exposures). There is no need to check or adjust the camera during the exposure — simply leave it in place until you're ready to retrieve it.

Optimal Exposure Periods

Short exposures (1–4 weeks) produce images with a small number of sun trails — each trail representing one day — against a relatively faint landscape. The trails are individually distinct and countable, and the weather pattern is clearly readable. These exposures work well as a first experiment because the results are available quickly and demonstrate the principle clearly.

Medium exposures (1–3 months) produce richer images with denser sun trails and a better-exposed landscape. The seasonal shift of the sun's arc becomes visible — the trails gradually rise (toward summer) or fall (toward winter) over the exposure period. The landscape detail is more pronounced because the cumulative exposure has had more time to differentiate between light and dark features.

The ultimate solargraph is a full-year exposure — December solstice to December solstice (or June to June, depending on hemisphere). A year-long exposure captures the complete range of the sun's annual motion: the low, short winter arcs near the bottom of the image, the high, long summer arcs near the top, and the gradual seasonal progression between them. The landscape is deeply exposed and shows surprising detail. The number of sun trails (one per day) reaches 365, creating a dense pattern that visually represents an entire year of solar motion and weather. Six-month exposures (solstice to solstice) capture half the annual range and are also very popular.

Retrieving and Scanning the Solargraph

At the end of the exposure period, retrieve the camera and take it to a dark room (not necessarily a photographic darkroom — any room without bright light will do, since you need only a few minutes of dim light to extract the paper). Open the can carefully and remove the photographic paper. The image is now visible on the paper as a negative — bright areas (sun trails) appear dark, and the landscape appears in reversed tones. The image is not fixed — it remains light-sensitive and will continue to darken if exposed to light. You have a limited window (typically 15–30 minutes in dim room light) to scan it before the image degrades.

Place the paper face-down on a flatbed scanner and scan at high resolution (1200–2400 dpi) in colour mode. Even though the photographic paper is nominally black-and-white, the photochemical darkening that occurs during months-long exposure produces colour — typically deep blues, purples, and violets in the sky areas, warm golden or amber tones in the sun trails, and earthy browns and greens in the landscape. Scanning in colour captures these hues, which are one of the most beautiful visual characteristics of solargraphs and are entirely natural — produced by the chemistry and physics of long-term photochemical reactions, not by any artificial colouring.

After scanning, invert the image in Photoshop or equivalent software (the scanned image is a negative; inversion converts it to a positive). Adjust levels, curves, and colour balance to taste — the raw scan is typically low-contrast with heavy colour casts that benefit from correction. Some photographers prefer minimal post-processing, letting the natural colours and softness of the solargraph stand; others adjust more aggressively for maximum visual impact. Both approaches are valid — the solargraph aesthetic accommodates a wide range of post-processing interpretations.

Fixing Solargraphs for Permanent Display

The paper itself, once scanned, will eventually darken to complete black if exposed to light, because the unfixed silver halide continues to reduce to metallic silver. Some photographers fix the paper after scanning (immerse in standard photographic fixer for 2–5 minutes, then wash and dry) to stabilise it — but fixing dissolves much of the image because the printing-out silver is less stable than chemically developed silver, so the fixed result is typically much fainter than the unfixed scan. The scan, not the paper, is the primary output of solargraphy — the paper is essentially a recording medium that is transcribed to digital form via scanning.

For display, print the scanned and processed solargraph digitally on high-quality inkjet paper, canvas, or metal print substrate. Solargraphs look particularly stunning printed large (A2 or larger) because the detail in the sun trails and landscape becomes more visible at scale. Printing on metallic paper adds luminosity to the sun trails. Canvas printing echoes the handmade, organic quality of the original pinhole process.

Creative Variations

Multiple pinhole solargraphy: pierce several pinholes in the can at different positions. Each pinhole projects a separate, overlapping image onto the paper, creating a multi-exposure effect with multiple sets of sun trails intersecting at different angles. The result can be chaotic but also remarkably beautiful — a kaleidoscopic astronomical record.

Wide-format solargraphy: use larger containers — paint tins, Pringles tubes, postboxes, or custom-built enclosures — for bigger images and wider fields of view. 8×10 or even 11×14 inch paper can be used in larger containers, producing solargraphs with remarkable detail and tonal richness.

Colour photographic paper solargraphy: using colour photographic paper instead of black-and-white produces solargraphs with different (and sometimes more vivid) colour characteristics, as the three colour-sensitive layers in the paper respond differently to the months-long exposure. The results are unpredictable and film-stock-dependent, but often strikingly colourful.

The Science of Sun Trails

The sun trails in a solargraph are a precise astronomical record. Each trail represents one day's solar transit across the sky, and its arc — its height, length, and curvature — is determined by the sun's declination on that date and the latitude of the observation point. At the summer solstice, the sun reaches its highest declination (23.4° north of the celestial equator in the Northern Hemisphere), producing the highest, longest trail. At the winter solstice, the sun reaches its lowest declination, producing the lowest, shortest trail. The trails between solstices show the gradual seasonal shift in the sun's path — a visual demonstration of the axial tilt of the Earth that drives the seasons.

Gaps in individual trails correspond to clouds blocking the sun — each gap represents a period of overcast weather. A solargraph from a rainy climate shows many interrupted, gap-riddled trails; a solargraph from a desert climate shows mostly complete, unbroken arcs. The overall pattern of complete versus interrupted trails is a beautiful, intuitive visual summary of the local weather over the exposure period — a satellite weather map encoded in silver chemistry by the sun itself.