Seeing Like a Pinhole: The Image, Its Makers and Previsualisation

Hold a pinhole negative next to one made with a lens and you can tell them apart across a room. The question this page answers is which optical fact produces each of the differences, and the reason it matters is that a trait you can trace to a cause is a trait you can use. Softness that comes from the hole diameter can be made larger or smaller by changing the plate. Dark corners that come from the cosine-fourth law can be pushed outside the frame by lengthening the camera, or dragged into it deliberately. A photographer who calls all of it “the pinhole look” has one setting; a photographer who knows where each part of it comes from has a dozen.

The second half of the page is the harder problem. Your camera has no viewfinder, no ground glass and no focusing to do. You have to decide what will be in the frame, from where, for how long, before you can see any of it — and the only way to be right more often than chance is to build the arithmetic into a piece of card and to write your intention down before you expose.

The rendering, and the cause of each part of it

Nothing in this section is new physics. Every line of it was derived in Part VI’s geometry lesson or the diffraction lesson; what is new is reading the derivations backwards, from the picture to the number.

One frame, six traits, six causes

1. 1Uniform unsharpness — b = d (1 + f/u); at infinity b = d, so every part of the picture is equally soft
2. 2No plane of focus — nothing converges, so blur has a floor and not a minimum
3. 3Dark corners — cos⁴ θ: exactly 2 stops at 45°, exactly 4 at 60°
4. 4Stretched near-far scale — m = f/u — a consequence of standing close, which a wide angle permits
5. 5Directional smear — image displacement = m × subject displacement during the exposure
6. 6White sky, dark reds — undyed paper responds in the blue and UV and stops near 500 nm

Five of the six are geometry and the sixth is chemistry. Each is attached to a quantity you set when you choose the plate, the frame, the viewpoint, the duration and the material.

Softness is uniform, and it has a size you chose. The blur circle is b = d(1 + f/u), which for anything more than a few focal distances away is just d. A 0.25 mm hole builds the whole picture out of 0.25 mm discs whether the subject is a doorway at 3 m or a hill at 3 km. That is why pinhole softness reads differently from a lens’s out-of-focus background: a lens gives you sharp somewhere and soft elsewhere, and the pinhole gives you the same everywhere. Wall’s 1912 dictionary puts the positive half of this plainly — the pinhole image “although unsharp, is not affected by” any of spherical aberration, chromatic aberration, distortion, curvature of field, astigmatism or coma, “to minimise which is the chief difficulty of the constructor of lenses”. Wall also names the one way you can reintroduce something aberration-like: pierce a slot instead of a round hole and the blur becomes directional, which he says pinhole workers “occasionally introduce”, calling it astigmatism although it is nothing of the kind. If your negatives are soft in one direction only, that is your hole, and the pinhole register from Part VI will tell you which plate did it.

There is no plane of focus, so there is no depth of field either. Both statements are the same statement. Nothing converges behind a pinhole, so blur has a floor rather than a minimum, and the familiar claim that “everything is in focus” is exactly backwards: nothing is, equally, everywhere.

The corners go dark, and the loss is exact. The cosine-fourth law costs 2.00 stops at a field angle of 45° and 4.00 stops at 60°, because cos 45° = 1/√2 and cos 60° = 1/2 make those two values exact rather than approximate. On 4 × 5 inch paper at a 50 mm focal distance the corner sits at 58.4°, and the corners are 3.7 stops down. Move to 80 mm and the corner comes back to 45.4°, losing 2.1 stops. The darkness of the corners is a dial, and the dial is the focal distance.

The near-far stretch is not the lens’s fault, it is yours. This is the trait people most often attribute to the wrong cause. Perspective — the relative sizes and positions of things — is fixed entirely by where the aperture is. A pinhole standing where a lens stood gives the same perspective the lens gave. What a short focal distance does is widen the angle of view so that you can stand 300 mm from a kerbstone and still have the far end of the street in frame, and it is that closeness that makes the kerbstone huge and the street small. The magnification is m = f/u, so a stone at 0.5 m and a facade at 20 m are rendered at scales forty times apart. Say it as the instruction it is: to exaggerate near against far, move the camera, and use the short focal distance to keep the far thing in frame.

Movement smears, and the smear has a length. During an exposure of t seconds a subject moving at v travels vt, and its image travels m times that. That is the whole of smear length, and the movement assignment makes a compositional tool of it.

On paper the sky is white and the reds are black. An undyed silver halide emulsion — which is what enlarging paper is — responds in the blue and the ultraviolet and gives out around 500 nm, as Part IV’s spectral sensitivity lesson establishes. A blue sky is the brightest thing in the frame to such a material, so it exposes heavily, goes dense on the negative and prints white; foliage and red brick reflect light the paper cannot use and go thin, printing dark. The nineteenth-century look of a paper negative is not nostalgia. It is the same chemistry that gave the nineteenth century its own pictures.

From the historical darkroom

Documented events in pinhole photography that this course has read at first hand

1856

Brewster describes the lensless camera

1889–91

Emerson · Davison · Rayleigh

1904–12

Petrie’s pinhole stop · Wall’s dictionary

1912–71

a gap in this course’s own reading

1971

Young, Pinhole Optics, Applied Optics

2001–

Worldwide Pinhole Photography Day

2012

Pinhole Resource archive to a museum

1850188019101940197020002030

A strip of events the course has verified at first hand, not a canon. Each row's label carries its date; the block widths are drawn so the labels can be read and are not durations. The gap between 1912 and 1971 is a gap in this course's reading and not a claim that nothing happened — that period is where the secondary literature places the pinhole's eclipse, and the primary material to confirm it has not been read here.

Brewster, 1856. The passage usually cited as the first published description of lensless photography sits in the middle of a chapter about stereoscopic portraiture. Brewster explains how an image forms through “a small aperture, H, in the side, M N, of a camera”, observes that pictures so made “are accurate representations of the object, whether it be lineal, superficial, or solid”, and then names the one error he can imagine: “the inflexion of light” — diffraction — adding that “we believe that it would exercise a small influence, if any, and it is only by experiment that its effect can be ascertained”. Rayleigh did that experiment thirty-five years later and got a number out of it. Brewster then records what he had actually done: he and the Rev. Mr Egerton “obtained photographs of a bust, in the course of ten minutes, with a very faint sun, and through an aperture less than the hundredth of an inch”. A hundredth of an inch is 0.25 mm, which is the middle of the range you pierced in Part VI. His conclusion is a prediction and an objection in the same breath: “when chemistry has furnished us with a material more sensitive to light, a camera without lenses, and with only a pin-hole, will be the favourite instrument of the photographer. At present, no sitter could preserve his composure and expression during the number of minutes which are required to complete the picture.”

That objection is still the first thing the portrait assignment has to solve, one hundred and seventy years later.

Emerson, 1889, and the argument about sharpness. P. H. Emerson’s Naturalistic Photography argued that photographic pictures should be made as the eye sees, not as the lens resolves. His phrasing is famous: “The great heresy of ‘sharpness’ has lived so long in photographic circles because firstly the art has been practised by scientists, and secondly by unphilosophical scientists.” His rule follows: “a picture should not be quite sharply focussed in any part, for then it becomes false; it should be made just as sharp as the eye sees it and no sharper”, and therefore “focus for the principal object of the picture, but all else must not be sharp; and even that principal object must not be as perfectly sharp as the optical lens will make it.”

Read that rule with the first section of this page in front of you and something jumps out. Emerson’s programme is differential softness — one thing rendered clearly because that is where the eye rests, everything else held back. A pinhole cannot do that. It gives one blur circle, the same size everywhere, with no way to make any part of the frame sharper than any other. Emerson knew what a pinhole was and dealt with it in three sentences on page 131: the drawing “would obviously be correct”, but “since the exposures required to produce pictures without lenses vary roughly from one to thirty minutes, this method cannot be seriously considered here” — though, he adds, “in cases where the length of exposure is immaterial, this method would be a worthy field for experiment.”

Davison, 1890. A year after that sentence was printed, George Davison exhibited a picture of an onion field on Mersea Island in Essex that became the flashpoint of the argument. The Victoria and Albert Museum holds it in the Royal Photographic Society Collection as The Onion Field, Mersea Island, Essex, photographed 1890, accession RPS.2369-2017, and records its materials and techniques as photogravure on paper, 155 by 205 mm. Two further Davison prints titled The Onion Field are in the same collection, dated 1890 and 1891. Davison went on to co-found the Linked Ring, the secessionist body through which Pictorialism did most of its arguing.

⁇Was The Onion Field made with a pinhole?

The claim that Davison’s picture was made with a pinhole is repeated in general reference accounts of his work and in the pinhole literature, and it is the reason he appears in every pinhole history.

What the museum record says is narrower. The V&A’s catalogue entry for RPS.2369-2017 gives the title, the maker, the year, the place and the medium — photogravure — and names no camera and no aperture. Photogravure is a printing process, so the record describes how the print was made rather than how the negative was exposed, and it neither confirms nor denies a pinhole.

What this course has not read is the period evidence: the 1890 exhibition catalogue of the Photographic Society of Great Britain, the photographic press of that autumn, or Davison’s own account. Without one of those the attribution rests on secondary summary.

What the course therefore does is state the museum record as fact and the pinhole as a widely repeated attribution it has not traced to a primary source. If you can consult the period press for 1890, that is a piece of research this course would like back. What is not in doubt, and is the part that matters for your own work, is that the argument of 1890 was about whether an unsharp photograph could be a good one — and that both sides were arguing about a picture nobody has shown this course was made the way the story says.

Petrie, 1904, and a correction worth making. Flinders Petrie’s Methods and Aims in Archaeology is often cited for pinhole photography in the field. Read the chapter and what he actually describes is subtly different, and more interesting. Petrie tells the excavator to “stick to one small stop, say f/100, and learn exposures entirely on that basis” — a working discipline this course would recognise as an exposure log with one variable removed. Then: “Small stops can be made out of a strip of tin plate or blackened card; and the hand camera can be stopped down with a pin-hole stop stuck in front of the lens so as to work at almost any nearness and scale with exposures of ½ or 1 minute in full sunshine.” That is a pinhole stop over a lens, not a lensless camera. He was buying the pinhole’s freedom from a plane of focus — “almost any nearness and scale” — while keeping the lens in place, and paying the usual price in minutes. Petrie belongs in this history, but for what he did rather than for what he is usually said to have done.

The revival, and what the course can and cannot date. Matt Young’s 1971 paper in Applied Optics treats the pinhole as “a useful and practical device” rather than a curiosity, and notes that its angular field “can be made to exceed 90°”. From roughly that point the lensless camera becomes an artist’s instrument again. Pinhole Resource, run by Eric Renner and Nancy Spencer, supplied materials and gathered an archive of pinhole photographs from artists worldwide; in 2012 it donated 6,000 photographs from 500 photographers, 60 cameras and 200 books and catalogues to the Palace of the Governors Photo Archives at the New Mexico History Museum, where more than 1,300 of them are now in the digital database. Worldwide Pinhole Photography Day falls on the last Sunday in April — 26 April in 2026, 25 April in 2027 — and its site carries a copyright range beginning in 2001, which is the earliest date this course can support for it. And solargraphy, the months-long print-out exposure that records the sun’s daily arcs, is the newest branch of all; the night assignment owns it, and owns the job of tracing its attribution properly.

📓Three things this course could not verify, and says so

Founding years for Pinhole Resource and the run of Pinhole Journal: the organisation’s site records what it holds and what it gave away but did not yield a founding statement this course could read, so none is printed. The organiser of Worldwide Pinhole Photography Day: named on the site only as “organizers and volunteers”. And the attribution of solargraphy’s origin to a Solaris project around 2000: repeated widely, not traced here to a primary publication. In each case the course prints the verified fact and leaves the gap visible rather than filling it.

Reading a pinhole photograph

Critique that stops at “I like it” teaches nothing. Reading a picture in this course means separating the maker’s decision from the medium’s accident, and the way to do it is to ask, of each visible feature, which number in the camera it came out of.

Work through a negative in this order.

1. Where is the aperture? Not what focal distance — where in space. Everything about the relative size of near and far things follows from it, and nothing else does. A picture whose foreground overwhelms it was made by a person who put the camera 300 mm from something, and that was a decision.
2. How big is the blur, in the picture’s own units? Measure a hard edge on the negative with a loupe. If the transition is about the width of your recorded hole diameter, the picture is geometry-limited and the plate is what set it. If it is much wider, something else is going on: camera movement, a slot rather than a round hole, or a subject that moved.
3. How dark are the corners, and does it match? Compare an even patch at the centre with the same material at the corner. Part VI’s table converts the field angle to stops; if your corners are worse than cos⁴ predicts, plate thickness is the usual reason.
4. What is missing? The people who walked through, the leaves that moved, the flag. The movement assignment makes that quantitative; here, just notice that absence is a record of duration.
5. What did the material decide? White sky, black foliage, a red door gone to nothing — those are the emulsion’s spectral response, not the photographer’s tonal judgement, unless the photographer chose the material knowing what it would do. Which is the point.

Only after those five does the interpretive question become answerable: of everything you have just listed, which parts look chosen? That is the whole difference between a photograph made with a pinhole and a pinhole photograph.

⁇Is pinhole softness atmosphere, or is it failure?

This one is genuinely open, and the course does not settle it.

Emerson’s position, 1889, was that a wholly sharp picture “becomes false”, and that a photograph should be as sharp as the eye sees and no sharper. On that argument the pinhole’s softness is truthful. But his own rule required differential focus, which a pinhole cannot give, so his position does not actually endorse the pinhole — and he said as much, dismissing it as too slow.

The opposing position, held by most of the photographic establishment Emerson was attacking and by most technical writers since, is that uniform unsharpness is a limitation to be minimised. Rayleigh was working in that tradition in 1891 when he looked for the best aperture: the question only makes sense if sharper is better.

What both sides in 1890 ignored is the fact this course derived in Part VI: the pinhole’s sharpness is set by the ratio d/f, and there is a diameter at which it stops improving because diffraction takes over. Softness is not one thing to be embraced or apologised for. It is a quantity with an optimum, and a maker can sit at that optimum, above it or below it on purpose.

What the course uses: neither position as a rule. It asks instead that you say, in the log, which blur you intended and why, and then measure what you got.

Framing without a viewfinder

Your camera sees between 57° and 146° across the diagonal depending on which frames are fitted. No human being can estimate that by eye. The fix is arithmetic transferred once into a piece of card.

angle = 2 arctan( w / 2f )

Angle of view, from Part VI

with w the width, height or diagonal of the sheet as the camera actually masks it, and f the measured focal distance. For 4 × 5 inch paper, 101.6 × 127 mm:

Focal distance	Across 101.6 mm	Across 127 mm	Diagonal
25 mm	127.6°	137.0°	145.8°
50 mm	90.9°	103.6°	116.8°
80 mm	64.8°	76.9°	90.9°
120 mm	45.9°	55.8°	68.2°

One card, three focal distances: the angle-of-view template

1. 1Long frame, 120 mm — cut the aperture to w × D / f, where D is the viewing distance on the string
2. 2Middle frame, 80 mm — halve the viewing distance and halve the aperture together when the card runs out
3. 3Wide frame, 50 mm and below — over 90° across the diagonal — use sighting notches, not a cut aperture
4. 4The knotted string — the template is only correct at the viewing distance it was cut for
5. 5The verification — check one template against a commissioning negative made from a known position

The template turns 2 arctan(w/2f) into a thing you can hold up. It is worth cutting once, marking with the focal distance it belongs to, and keeping in the camera bag with the pinhole register.

Cutting one. Choose a viewing distance D you can repeat — a knotted string taped to the card and held to your cheekbone is more repeatable than “arm’s length”. Then the aperture dimension is w × D / f: at D = 300 mm, the 120 mm frame’s 101.6 mm side becomes 101.6 × 300 / 120 = 254 mm. Above about 90° the aperture stops fitting on any card you can hold, which is a fair warning that the wide settings need a different tool.

The string-and-card finder is that tool. Two notches on the card’s top edge, cut at half the frame width for the same D, define the left and right edges directly: line one notch up with what you want at the left of the picture and the other with what you want at the right, and everything between them is in. It is cruder than a template and it works at any angle.

A phone as a preview. A phone camera reports a 35 mm-equivalent focal length, which is a statement about angle of view relative to the 43.27 mm diagonal of a 24 × 36 mm frame. Matching your pinhole camera to it is one line:

f_equiv = 43.27 mm × f / (diagonal of your sheet)

Equivalent focal length for a preview

The equivalent focal length is the number to set. On 4 × 5 inch paper: the 120 mm frame previews at 32 mm equivalent, the 80 mm frame at 21 mm, the 50 mm frame at 13 mm — which is the ultra-wide camera on a phone that has one — and the 25 mm frame at 6.7 mm, which no phone offers, so at the widest settings the preview simply is not available and the template or the notches have to do the work.

Two cautions. The aspect ratios differ, so matching on the diagonal leaves the edges wrong: 4 × 5 is squarer than 3 : 2, so the phone will show you more at the sides and less top-and-bottom than the sheet will record. If the picture depends on one dimension, match on that dimension instead — 36 mm × f / 127 mm for the long side, 24 mm × f / 101.6 mm for the short. And a phone preview shows you the framing and nothing else: not the softness, not the corner falloff, and not what a two-minute exposure will do to the things that move.

Where the camera goes

Three placements are the pinhole’s native ground, and all three follow from what the previous sections derived.

On the ground. With no viewfinder to look through and no need to focus, there is nothing stopping you putting the camera on the pavement. At 50 mm on 4 × 5 paper the frame takes in 104° across its long side, so a camera lying on a kerb with the sheet upright includes the paving immediately in front of it and the top of the building opposite. Nothing else in this course sees like that.

In the extreme foreground. Because blur has a floor rather than a cliff, a subject at two focal distances is blurred only 1.5 times as much as a distant one. A stone 100 mm from a 50 mm camera is rendered at half life size and is still recognisable. There is no lens in this course that will do that without extension tubes and a bellows factor.

Levelled, with the hole shifted. Tip the camera up to include a roofline and the verticals converge, exactly as they would behind a lens, for exactly the same reason: the film plane is no longer parallel to the building. Slide the pinhole up instead, parallel to the film, and the whole image circle slides with it — nothing rotates, so verticals stay vertical. This is the view camera’s rising front, and Petrie, who had no time for complicated apparatus, called the sliding and rising front “about the only complication that is useful in serious work”. The architecture assignment computes what it costs at the corners, which is where the pinhole shift runs out.

And one placement to think about rather than adopt: the horizon on a flat back sits where you put it, and it stays straight. On the curved back only the horizontal at the pinhole’s own height stays straight, and everything above and below it bows. Choosing between them is choosing a cylindrical mapping or a flat one, and the panorama assignment makes that the subject.

Duration as a compositional choice

At f/200 on paper, the shortest useful exposure outdoors in bright sun is around a minute, and indoors it is tens of minutes. You do not get to choose a short exposure. What you get to choose is how long, and that choice decides what is in the picture as surely as where you point it.

The rule to carry, made quantitative in the movement assignment, is this: a subject that occupies a given patch of the frame for a fraction of the exposure contributes that fraction of the light at that patch, and the background contributes the rest. Two consequences follow immediately and both are counter-intuitive.

A person walking past does not appear at all — not because they are moving fast, but because at any one point in the frame they are present only for as long as it takes them to walk their own width. Half a metre at 1.2 m/s is 0.42 seconds, and 0.42 seconds out of a four-minute exposure is 0.17 per cent of it. And a person who stands still for half a four-minute exposure is not half-visible either: if they are much darker than the wall behind them they take about three-quarters of a stop off that patch, which on paper is a distinct but transparent ghost. Getting a solid figure needs most of the exposure, not half of it.

The composition question, then, is not “how long an exposure will this need” but “what do I want present, and for what fraction?” — and that is a question you answer before you open the shutter, in the log, in seconds.

Choosing the material, the hole and the focal distance for the picture

Four decisions, in the order they constrain each other.

Material first, because it sets the palette and the speed. Paper negatives are cheap, blue-sensitive, and roughly ISO 3 to 6 by ILFORD’s own equivalence for MULTIGRADE RC — so white skies, dark foliage, and exposures in minutes. Panchromatic sheet film sees the whole spectrum, is a hundred times faster, and comes with published reciprocity data, which is why the filter and night work needs it. A plate you coated in Part V has whatever speed and colour response you built into it, and no number until you bracket one; its interest is that the material is part of the picture’s authorship.

Focal distance second, because it sets the angle and the corners together. You cannot have the wide angle without the dark corners; the cos⁴ table is the exchange rate and it never varies.

Hole third. Part VI’s optimum, d ≈ 1.56√(λf), is the sharpest hole for a given focal distance, and there is nothing wrong with sitting off it deliberately: a smaller hole is slower and no sharper, a larger one is faster and softer, and a deliberately softer picture that cost you a stop of exposure time may be exactly what a moving subject needed. Write down which you chose and why.

Duration last, because it is the one you can still change while the shutter is open.

The log as the instrument of intention

Part VI’s exposure log had ten fields written before the shutter opened and five after, and its purpose was measurement: a season of rows yields your paper’s effective speed and its reciprocity trend, neither of which anybody publishes. Every one of those fields still applies here. What the assignments add is a field Part VI did not need.

The intention. One or two sentences, written before the exposure, saying what the picture is meant to be — not what is in front of the camera, but what you want a viewer to notice, and what you expect the medium to do to it. “The kerb stretching away with the church small at the end of it; paving sharp-ish in the near corner; the two people at the bus stop will not record.” That is an intention, and it is falsifiable, which is the entire point. After processing you can say which clauses came true.

This is what makes previsualisation teachable rather than mystical. It is not a picture in the mind’s eye. It is a written prediction with enough specifics in it to be wrong.

📓The three fields the assignments add to the Part VI log

Intention, above, written first. Predicted rendering of anything that moves, as a fraction and an expected tone, because that is the prediction the movement, portrait and night assignments are assessed on. And the reconciliation, written after the working positive is made: for each clause of the intention, did it happen, and if not, which number was wrong. A log that records only what you did is a diary. A log that records what you expected is an instrument.

Working positives, and why the fine print waits

A paper negative is hard to judge. Tones are inverted, the paper base is opaque, and the eye is bad at reading density through a reversal. So every assignment in this part ends with a working positive — not a print, a reading aid.

The quick route is to photograph the dry negative against a window or on a light box with a phone and invert it in any editing application, exactly as the commissioning experiment established. It costs nothing and it is honest as a reading aid, provided you remember that the phone has applied its own tone curve and that judgements of contrast made from it are approximate.

The better route is a contact print: negative face-down on a second sheet of paper, under glass, exposed to a bare lamp and processed in the same trays. It gives a real positive on real paper, and it introduces the losses of contact printing, so what you judge is closer to what a print will do.

Neither is a fine print, and neither is meant to be. Dodging, burning, grade choice and the whole craft of the print are Parts XVIII and XIX, and doing them badly now would only teach you to blame the negative for the printing. What you need here is enough of a positive to answer one question: did the intention happen?

Recap

• Six visible traits, six causes: uniform softness from b = d(1 + f/u); no plane of focus because nothing converges; corners from cos⁴ θ, exactly 2 stops at 45° and 4 at 60°; near-far stretch from the viewpoint, which a wide angle merely permits; smear equal to m times the subject’s travel; and white skies from a material that stops near 500 nm.
• Wall’s 1912 dictionary is the clearest period statement of the compensation: the pinhole image is free of every aberration a lens designer fights, and its one self-inflicted defect is a slot instead of a round hole.
• Brewster, 1856 described the lensless camera, photographed a bust through a 0.25 mm hole in ten minutes, anticipated diffraction as the only source of error, and named the sitter’s patience as the obstacle.
• Emerson, 1889 attacked “the great heresy of sharpness” but demanded differential softness, which is the one thing a pinhole cannot supply; he dismissed the pinhole as too slow and called it “a worthy field for experiment”.
• Davison’s 1890 picture is in the V&A as The Onion Field, Mersea Island, Essex, a photogravure; the museum record names no camera, and this course marks the pinhole attribution as untraced.
• Petrie, 1904 used a pinhole stop in front of a lens, not a lensless camera, and worked to a fixed f/100 so that his exposure knowledge accumulated. That is an exposure log with one variable removed.
• Frame with arithmetic: an angle-of-view template cut to w × D/f, sighting notches beyond 90°, and a phone set to 43.27 × f / diagonal for a preview that shows framing and nothing else.
• Choose material, then focal distance, then hole, then duration — and write the intention in the log first, in terms specific enough to be proved wrong.

Check your understanding

Question 1. You want the same building to fill the same fraction of the frame, but with the foreground paving rendered much larger relative to it. What do you change?

• Fit a shorter focal distance and stay where you are
• Move the camera closer to the paving, and fit a shorter focal distance to keep the building in frame
• Fit a longer focal distance and move back
• Use a larger pinhole, which increases the near-far difference

Show the answer and why

Answer: Move the camera closer to the paving, and fit a shorter focal distance to keep the building in frame

Relative size is perspective, and perspective is set only by where the aperture sits. Changing focal distance from the same spot changes the angle of view and the image scale, and crops or extends the frame — but the paving and the building keep exactly the same size ratio, because both magnifications m = f/u scale by the same factor. Moving closer changes u for the paving enormously and for the building hardly at all, which is what produces the stretch; the shorter focal distance is then needed only to keep the building inside the frame. Option 4 confuses blur with scale: the hole diameter sets b = d(1 + f/u) and has nothing to do with magnification.

Question 2. A negative made on 4 × 5 inch paper at a 50 mm focal distance shows corners about 2 stops darker than the centre. What does that tell you?

• The falloff is as predicted, since 2 stops is the cos⁴ figure for this format and distance
• The falloff is much less than predicted, so the measurement or the geometry is wrong
• The falloff is much worse than predicted, and plate thickness is the likely cause
• Nothing — cos⁴ applies only to lenses

Show the answer and why

Answer: The falloff is much less than predicted, so the measurement or the geometry is wrong

The half-diagonal of a 4 × 5 sheet is 81.3 mm, so at f = 50 mm the corner field angle is arctan(81.3/50) = 58.4°, and −4 log₂(cos 58.4°) = 3.7 stops. Two stops is far better than the law allows, and since real pinhole falloff is generally worse than cos⁴ rather than better — plate thickness adds a tunnel effect on top of it — something in the reading is wrong. The usual culprits are measuring a corner that is not really at the corner, a patch of subject that was not evenly lit, or a focal distance longer than you think. Exactly 2 stops would be right at a 45° corner angle, which on this format needs f = 81 mm.

Question 3. Emerson attacked sharpness in 1889 and Davison exhibited an unsharp picture in 1890, yet Emerson had already dismissed the pinhole. Which optical fact reconciles those two positions?

• The pinhole was too slow for the plates of the period, which was Emerson's only objection
• Emerson wanted differential softness, and a pinhole renders everything with one blur circle of the same size
• A pinhole introduces astigmatism, which Emerson considered a fault
• Emerson's rule applied to portraits only, and Davison photographed a landscape

Show the answer and why

Answer: Emerson wanted differential softness, and a pinhole renders everything with one blur circle of the same size

Speed was the objection Emerson wrote down — one to thirty minutes — but it is not the interesting one. His rule was to "focus for the principal object of the picture, but all else must not be sharp", which requires the picture to be softer in some places than in others, tracking where the eye rests. A pinhole cannot obey it: b = d(1 + f/u) is essentially d everywhere beyond a few focal distances, so the blur is the same at the point of interest and at the edge. The pinhole is therefore not the extreme case of Emerson's programme but a different proposition altogether, which is worth knowing before you invoke his authority for your own soft negative. Option 3 misreads Wall: it is a slot rather than a round hole that gives directional blur, and Wall says the name astigmatism is wrong for it anyway.

Question 4. You are photographing a busy square for four minutes at f/200 on paper. A friend agrees to stand still in the frame. To record as a solid figure rather than a faint ghost, roughly how long must they hold?

• About 30 seconds — the eye is very sensitive to a dark shape
• About 2 minutes, since half the exposure gives half the density
• Most of the four minutes; half the exposure costs the patch under a stop
• It makes no difference, because the paper's reciprocity failure cancels the effect

Show the answer and why

Answer: Most of the four minutes; half the exposure costs the patch under a stop

The light arriving at that patch is the sum of two contributions: the figure for a fraction φ of the exposure and the background for (1 − φ). If the figure is about a fifth as bright as the wall behind, the patch receives φ × 0.2 + (1 − φ) of what the bare wall would give it. At φ = 0.5 that is 0.6, which is log₂(0.6) = −0.74 stop; at φ = 0.9 it is 0.28, or −1.8 stops; only at φ = 1 does the figure get its full −2.3 stops. Presence is linear in the light, but "half the time" is nothing like "half the density", and it is the shortfall at the top of that curve that makes long-exposure ghosts so hard to place deliberately. Reciprocity failure and the shape of the characteristic curve both bend the relation between that light and the density you finally see, which is why the movement assignment brackets rather than trusting the arithmetic alone.

Check my answersClear