Part VI Overview: Build a Pinhole Camera

Everything so far has been knowledge. This part produces an object, and then a photograph made with it. The object is a camera with no lens in it, and it is worth five sessions of your time because a lensless camera is the only camera whose every dimension you can calculate from first principles and then check against the negative it makes.

That is the discipline here. You will derive the blur circle, find the hole diameter at which diffraction starts to cost more than it saves, compute the effective f-number and the corner falloff for your chosen format, cut the parts to those numbers, measure what you actually built, and then photograph a wall to see whether the prediction held. When it does not — and for a first camera it will not — the gap between prediction and negative is the finding, not the failure.

The camera is modular, and that is an experimental decision

The body you build carries interchangeable pinhole plates, extension frames that set three different pinhole-to-film distances, and backs that can be flat or curved, for paper, sheet film or a plate you have coated yourself. It has a light-trapped shutter, a tripod bush and a blackened interior.

None of that is convenience. Later pages change one of those things at a time and hold the rest still: a pinhole-diameter series at fixed focal distance, a focal-distance series at fixed pinhole, a flat back against a curved one with everything else identical. A camera whose hole is a hole in its own front panel cannot run those comparisons, because changing the hole means building a second camera, and a second camera differs in a dozen ways you did not intend. Modularity is what makes a controlled series possible with one instrument, and it cannot be added afterwards.

The modular camera, and the optical variable each part controls

1. 1Pinhole plate, interchangeable — sets d — the f-number and the sharpness limit
2. 2Shutter, light-trapped — sets time only; it must change nothing optical
3. 3Body, blackened inside — sets flare — the non-image light on the negative
4. 4Extension frames, stackable — set f — angle of view, image size, f-number and falloff, together
5. 5Back, flat or curved — sets the recording surface — how straight lines map

Read top to bottom as the light travels. Each element owns one variable, which is what makes a one-variable experiment possible with a single camera.

What you make, and what you measure

Two things are made: a graded set of pinholes, pierced in thin metal at roughly 0.2, 0.3, 0.4 and 0.5 mm, each mounted in an identical plate so that swapping one changes the hole and nothing else; and the camera itself.

Everything is measured. Each hole goes into a pinhole register with its diameter, the method used, the uncertainty of that method and the effective f-number it gives at each planned focal distance. Three independent routes are used — a scan at known resolution, a reticle loupe, and the diffraction pattern thrown by a Class 2 laser pointer — because a single number with no second opinion is not a measurement, it is a hope. The three disagree by a few per cent, and the size of that disagreement is the real content of the exercise.

What gets exposed

Five series, in order: a leak and flare test with no image at all, which the camera must pass before anything else is attempted; a bracketed exposure series, establishing what your paper needs at f/200 or thereabouts; a pinhole-diameter series; a focal-distance series; and a flat-against-curved-plane comparison. All on paper negatives, which are cheap, plus one sheet-film run processed here so that the chain from exposure to a dry negative has been done once.

The hand-off from Part I, and what you need first

The box you built for the camera obscura was specified to survive until now: rigid, with a replaceable aperture plate rather than a hole punched in the box. It can be the first body, and the qualitative observation you made there — that a smaller hole is sharper and dimmer until it stops being sharper — is exactly the trade this part turns into arithmetic. Lord Rayleigh set the two effects against each other in 1891, taking the summed blur from Petzval’s 1857 report; this part does the differentiation they did and gets a number out of it.

From Part IV you need the latent image, reciprocity and the life of the latent image — which matters here more than anywhere so far, because pinhole exposures are long — spectral sensitivity, which is why the optimum hole for blue-sensitive paper is smaller than for film, and the tray-processing routine of the latent image made visible. None of that is re-taught here.

Safety, cost and the route for people who cannot build

⚠The hazard envelope of this part

Everything practical here is Level A: hand tools, craft knives, needles, adhesives, paint, and the paper-processing chemistry Part IV already established. Nothing in this part needs a fume cupboard. The one hazard that is new is a Class 2 laser pointer, used only to measure a pinhole. UKHSA classify Class 2 as visible light that is hazardous on deliberate staring rather than on a momentary glimpse, and warn that pointers marked Class 2 are commonly found to measure as Class 3B or Class 4. The measuring page treats that finding as the design constraint it is: the beam never travels at head height, never meets a reflective surface, and is terminated on a matt wall.

If you cannot build, the optics still stand. The two optics lessons and the exposure lesson are complete on their own, and every calculation in them can be done for a camera you buy or a tin you already own. A biscuit tin, a stiff cardboard box and a commercially made pinhole body are all accepted routes; what is not optional is knowing the numbers for whatever body you use.

Three cost tiers run through the part: minimal (a tin or card box, a needle-pierced hole in drinks-can aluminium, paper negatives), recommended (a plywood modular body with stacking frames), and the two upgrades worth their money if the budget stretches — a bought laser-drilled pinhole and a second-hand 4 × 5 inch film holder. Dated prices live in the laboratory planner rather than in these pages, so they can be corrected without rewriting the course.

The pages of this part

Part6 of 28Level2 — PractitionerPages10Estimated time21.8 hoursHighest safety levelLevel A

✱4 of 10 pages in this part need a darkroom, a UV source or mains-powered equipment, marked below. Each says what can be improvised and, where one exists, gives an alternative route.

0 / 10 lessons in this part completed

• LessonPinhole Geometry: Blur, Focal Distance, Field of View and Falloff55 min
• LessonDiffraction and the Optimum Pinhole60 min
• LabMaking and Measuring PinholesA120 min
• LessonDesigning the Modular Camera50 min
• BuildBuild the Modular Pinhole CameraA300 min
• LessonPinhole Exposure and Reciprocity Correction60 min
• ExperimentCommissioning the Camera: Light-Tightness, Flare and the First NegativesA✱ Darkroom240 min
• LabLab: Processing Your First FilmA✱ Darkroom150 min
• ExperimentCurved Film Plane and Multiple-Pinhole ExperimentsA✱ Darkroom180 min
• Break/fixBreak/Fix: Unexpectedly Soft Images and Wrong Reciprocity CorrectionsA✱ Darkroom90 min