Photography, its principles and applications

Preface

TO THE EIEST EDITION

A writer comes to the end of the making of his book, filled — as Carlyle might have said — with a divine discontent at the way he has marshalled his fragments of knowledge of an overflowing subject, and then sits down to write the forewords.

In my case, the impression is that of bringing home a drove of pigs from market, some tied by the hind legs with strings, many times on the road crossed and twisted ; others darting into holes and corners where they had no business, and having to be fetched out. And now, dusty and tired, with my little herd safely confined in their separate pens, you, my reader, come along, fresh, alert, and critical, and I know not whether you will see what you expect to find.

To forsake metaphor, it is a mere truism to say that photography has so expanded its limits that every class uses it, and perhaps each one from a different motive. Is it the schoolboy, snapping his sisters or schoolmates with a Brownie bought yesterday ; or the astronomer, wishing to make star records? The traveller, seeking records of the people, customs, architecture, and landscape beauties of the country through which he passes, that he may embody them in a book or lecture ; or the experimenter dipping into the records of early investigators, and

VI

PEEFACE eager to be in touch with even small discoveries ? When in 1890 I saw Frese-Green exhibit at Chester the first moving film picture (it was merely a human hand opening and shutting) I could not predict that the idea would expand until moving photographs would constitute the most widely used form of all entertainment.

There are my own memories of changes and progress. I write this in a Radnorshire roadside inn ; the landlady comes in with the bedroom candle ; and I bring to mind the day thirty-five years ago when she first came to the inn, for I called on her that very day. It was on a business-driving journey, and in the trap was my wet plate photographic kit. What a proceeding it was in those days ; the pitching the portable tent, sitting on one’s heels inside, drawing the flaps, coating the plate with collodion, dipping it in the silver bath to sensitise, carrying out to expose, not far away, for it must be developed while still wet, again cramped, within the low tent. And yet with all the obstacles difficult subjects were attempted. Over the other side of that great mountain mass — the Radnor Forest — I remember turning out one cold winter’s morning and taking scenes on the little frozen stream with the trees hung with hoar frost, and a lighted spirit lamp required in the tent to thaw needles of ice in bath and developer. Those were simple days, when lantern slides and negatives of moving subjects were alike made on one sensitive film — wet collodion — and varying “ speeds of plates ” were almost unknown.

To-day, in place of this heavy load, I carry a vest pocket camera with plates (no need to call them “dry” plates

PREFACE

Vll any longer, for the present generation have forgotten the “ wet ” process) ready prepared, and enlarge to a respectable size in an always ready box enlarger.

The limits of one handy volume have prevented the introduction of matter which might perhaps be thought necessary to make a book on photography complete. I should have liked to have written on the evolution of the art : how the Britisher, as usual, fell upon his feet in the keen competition in discovery during its early history ; how the negative process independently discovered by Fox- Talbot was the real parent of present-day photography, while the beautiful method of Daguerre died without succession. How for a long time inventive progress was chiefly British ; but how German thoroughness (in developers and dyes especially) and French cleverness (as in the autochrome) have brought other nations up in the race.

Another forced omission is the picture-making aspect of the handicraft. Perhaps it is as well, for who since H. P. Robinson has been really helpful to that very considerable body of workers who try to interpret their individual impressions with the aid of the camera ? And it may be, too, that I should have been drawn into the ever recurring question of whether photography can be called a fine art, and would have to explain the only answer I can suggest, namely, that it is so if you can find the genius who makes it a fine art.

Nothing, too, will be found in these pages on such matters as mounting and framing, for this volume makes no attempt to be a complete handbook.

Neither have I attempted to compile a cyclopaedia, with

PREFACE viii

information culled from many contributors, each approaching the subject from a different standpoint.

I may be wrong, but a book embodying the individual attitude of one mind towards a very diversified subject, and forming a revealment of the pigeon-holes of his brain, may with its inevitable errors and omissions have its advantages over a more complete but compiled volume. The greater attention given to my own methods in exposure and development will, I am sure, be forgiven.

A. W.

NOTE TO THE SECOND EDITION

The book has been revised throughout.

In the five years which have gone by since it was written, I seem to find photography taking its place in an Homeric epoch. I see Ponting recording with his cine camera the heaving prow of the Terra Nova as she crushes through the ice, and Scott waving his hand in last farewell as he disappears in the snowy distance. I see Bowers pulling the string to record that last group at the South Pole. I see Hurley of the Shackleton Expedition filming the final plunge of the Endurance as she goes down among the ice-floes. I see the army film man of the Somme advance, recording the movements of the wounded and the stillness of the dead, standing up above the parapet as the men spring to the assault, some to slide back in death-throes almost at his feet. And I see the camera men of the Royal Flying Corps, with shells bursting around them in the air, calmly swooping low and securing systematic survey negatives of enemy trenches and gun positions, and so helping to save lives in our next advance.

The photographer is not out of it in these days of “ men that are men again.” A w

CHAP.

Contents

PAGE

PREFACE V'

I. FIRST PRINCIPLES .1

Chapter I

Of all the useful arts, not one has received a more happy or exact name than Photography. Drawing by or with light describes precisely the work of the photographer. And although at first sight it may appear that he who photographs has had the work made possible by investigations in two apparently distinct branches of science — optics and chemistry — it will soon be seen that a study of the properties and behaviour of light rays really covers the whole matter.

The easiest way to commence inquiry into the governing principles of photography is to take a simple practical case, and to inquire the why and wherefore of the means which present-day knowledge uses to attain the desired end.

A Simple Photographic Problem.

An object or subject — say a human figure — is placed in the full light of sun or sky out of doors, the camera is set up pointing towards the subject, a lens being fixed in the front of the camera and a sensitive plate at the back. It is desired to obtain such a photographic image on the plate

p. b that it may be, not a finished photograph in itself, but a means of producing any number of photographs from itself. In other words (for we cannot escape from technical words which must be defined later), it is desired to take a photographic negative from which a number of positives or prints can be made afterwards.

This simple problem is really the central operation from which the multitudinous applications of modern photography diverge, and its principles must be mastered as a foundation of the whole subject.

The first fact which governs this problem is that light is an absolute essential, and the dominant force of the whole matter. Wait until the darkness of night comes on, and it is impossible to photograph unless an artificial light (as magnesium light or electric light) is introduced. It is not the subject which “ takes the photograph,” but the light which falls upon the subject. It was through study of the laws and properties of light by scores of investigators for some generations past that photography has been made possible, and a mere study of various cameras and lenses and sensitive plates and developers does not — without some knowledge of the laws of light — form a groundwork of an intelligent appreciation of photography.

The chief influences which govern our simple problem are as follows : —

1. Light , emitted in rays from a light source (in this case sun or sky).

2. Subject (in this case a human figure), reflecting rays of light.

8. Lens , receiving and bending rays of light to form image (of human figure) in the camera.

4. Sensitive plate, receiving rays of light forming image, and recording the image by chemical change.

It will be necessary to consider these matters in detail under thes«8 headings, and it will be seen that the path of one ray of light can be traced, like a continuous thread, through the whole problem.

Light. — It is only necessary to consider in this place those properties of light which are concerned in our simple photographic problem. Light is a form of motion emitted from a light source, which is usually an incandescent or highly-heated body. The greatest light source is the sun, which is often shut off from our view by clouds or other vapours round the earth. These clouds or vapours reflect and transmit sunlight to us, and become secondary light sources.

Light moves in straight lines as long as the medium through which it passes is unaltered, and can pass through many solid substances such as glass, gelatine, celluloid, etc. In considering light it is best to think of a single beam or ray. For instance, out of doors we should not notice that light moves in straight lines, as it appears to be diffused everywhere. But go up into an attic or loft where a beam of sunlight has found its way through a chink in the roof, and its straight path (shown up by reflection from dust particles, for a ray of light not impinging on the eye is invisible) will be very plain. Hold a mirror in the path of the beam of light, and it will be reflected in another direction, still in a straight line. Hold a white handkerchief in its path, and it will be broken up and reflected in all directions, some of the reflected rays reaching the eye and enabling you to see the handkerchief. Hold a bowl of water so that the beam of light falls into it, adding a little milk to the water, and the path of the beam of light will be plainly seen to be bent or refracted as it enters the water. Hold a cut glass decanter in the path of light, and a variety of colours will be seen if the decanter is moved about, this being caused by the cut surface forming a number of prisms, and separating the white beam into its component colours. Hold a dead black cloth in the beam of light, and there will be scarcely any reflected, almost all being absorbed. A blue

b 2 cloth would have the property of absorbing all but the blue rays, which are reflected to the eye.

The above experiments can be tried at night by placing a lighted bicycle lamp on a shelf, and shading it by a sheet of brown paper pinned to the shelf, a small hole being cut in the paper a little below the level of the flame.

These simple experiments have revealed several properties of a beam of light not yet fully explained. It is not necessary at this point to fully consider the fact that a ray of light is a bundle of complex vibrations, and that when we separate these vibrations, as with a prism, or by reflecting from an object which absorbs some of the vibrations and reflects others, a physical effect is produced on the eye which we call colour. The total effect of all the vibrations on the eye is that of white light.

The chief laws regarding light were laid down with remarkable accuracy by Sir Isaac Newton about 1675.

Subject. — This (in the case under consideration) is a human figure, standing out in the open air and receiving rays of light from all directions. The light falling upon it is white, and this it reflects in every direction, but not without alteration. Different parts of the figure have different capacities for absorbing certain vibrations and reflecting others. The boots, for instance, absorb equally almost all the vibrations, and reflect nothing (except a little white light from the polish at a particular angle). We therefore call the boots black. A blue tie absorbs ail the vibrations producing other colours and reflects to the eye (and to the camera) just that set of vibrations which we call blue. A white collar reflects equally all the vibrations and absorbs equally only a small proportion of each.

As we see in straight lines, it follows that we see the exact area and shapes of the patches of light and colour which are reflected from the subject, and therefore we are said to see the subject in all its complexity of shape and colours and shades, although it is only the various lights which we see. It will presently be plain to the reader that the photographic lens “ sees ” in exactly the same way as the eye. The brilliancy of the light reflected is in exact proportion to the brilliancy of the light illuminating the subject.

We are so accustomed to consider colours as appertaining to the subject instead of to the light, that the following experiment will prove instructive. Take a "white tea cup into a room lit only with a bicycle lamp. The cup will appear white as it reflects all the vibrations alike. Hold a sheet of blue glass in front of the light, and the cup (which still reflects all the light vibrations falling on it) will appear to be blue. With a red glass the cup will appear to be red. Now take in a blue cup and hold the red glass in front of the lamp. The capacity of the cup for reflecting blue light is now of no avail, for all the blue vibrations have been cut out of the light falling upon it by the red glass. The cup will now reflect little or no colour. This experiment shows that colour lies in the light and not in the subject.

Lens. — We have now come to that part of our problem which concerns the formation of an optical image in a darkened box or chamber by means of a lens (a piece of glass shaped like a lentil grain).

The camera obscura had been known for generations before the invention of photography. Porta, an Italian, discovered centuries ago that by making a very small hole in the shutter of a room otherwise perfectly darkened an image of the outside landscape was depicted on a whitened wall or screen opposite the hole. This image was reversed and in natural colours. Porta afterwards discovered that with a larger hole and a convex lens placed in it a more brilliant image resulted. But the pinhole method of forming an image without the use of a lens is so interesting, and forms such an easy step to understanding the action of a lens, that it is well to devote a moment to it.

In Fig. 1 E C D is a light-tight box with a small pinhole (say the size of a No. 5 needle) pierced in a thin brass plate in the front end. The back end may be supposed to be filled with a sheet of finely ground glass at C D. The

A

Fig. 1. — Formation of camera image.

subject to be photographed A B is represented (as in Newton’s time-honoured diagrams, which indeed are not yet out of date) by an arrow. An image of the arrow will be formed (upside down) on the ground glass at C I). To

Fig. 2. — Larger camera image.

understand why this image is formed, and why it is wrong side up, place the eye at D, and it will only be able to see (through the pinhole) a minute part of the point of the arrow A. In like manner the eye at C can only see a minute portion of the arrow head at B, and the eye at G can only see a bit of the arrow shaft at F,

Fig. .‘3. — Refraction of light rays.

The size of the image in the camera (as the box is called) is decided by the distance from E to G. This is shown in Fig. 2, where, the distance E G being more than in Fig. 1, and the camera being also made larger (from C to D), the image of the arrow is larger.

Although a pinhole as described is a practicable way of forming an image for photography — as will be shown in a future chapter — it lets in too little light to be generally useful, and does not give perfect definition.

A lens is therefore almost always used. A lens acts by bending or refracting the light rays. In Fig. 3 a ray of light A B is bent as it enters a thick piece of glass at B. But the edges of the sheet of glass being parallel, it is bent again in the opposite direction as it emerges at C, and so is unaltered in its general course. But if the edges of the glass are not parallel, if in fact we use a prism as in Fig. 4, the ray of light will be permanently bent after passing through the glass. Although a lens has a curved surface it may be regarded as a number of prisms of different angles joined together.

The result is that a number of rays of light proceeding from one illuminating point and falling upon different parts of the surface of the lens will be so refracted that after emerging from the lens they all meet together again at a point called the focus of the lens. This is shown in Fig. 5 (borrowed from Newton’s Opticks), where the various rays of light reflected from one point P of the subject and falling on different parts of the lens A B are so refracted that they meet together at a point p, and there form a sharp image of the surface from which they were reflected. In the same way sharp images of the

Fig. 4. — Prismatic refraction.

points Q R are formed at q r. In short, a complete image of the subject P R is formed at the plane r p, and the photographic process consists of placing a sensitive plate at this plane and securing the optical image.

Substances other than glass might possibly be used for making a lens, but in practice glass is almost invariably used. In two exceptional cases (Sutton’s panoramic water lens of about 1860 and Dr. Griin’s lens of the present time)

liquids have been enclosed within the lens to form part of the optical system.

A photographic lens has surfaces which are always portions of a sphere.

Unfortunately, the simple lens of one piece of glass having two convex surfaces (as shown in Fig. 5), and called a double convex lens, has a number of imperfections when used for photographic purposes. These imperfections — usually called aberrations in a lens — will be alluded to in another chapter, and for the present it is sufficient to note that a photographic lens even in its simplest form consists of at least two pieces of glass of different compositions, often cemented together. Also that in most cases two such lenses, forming a compound lens, are used together, and that a contraction in the opening of the lens (called a stop or diaphragm) is usually necessary.

The camera is a light-tight box which prevents any light falling upon the sensitive plate, except that which passes through the lens during the short space of time which is called the exposure. Its various fittings and adjustments enable the photographer to see the lens image on a ground glass screen before exposure, and to adjust accurately the sensitive plate in the focus of the lens.

Sensitive Plate. — We have been concerned hitherto in tracing the optical part of our simple problem, that is, the course of a ray of light from the time it issues from the light source until it assists in forming (inside the camera) an image of the human figure which is standing in front of the lens. We have now to touch upon the chemical side of our problem. Many substances darken, although slowly, under the action of light. The bleached paper on which our daily papers are printed will become darker under a day’s exposure to sunlight.

Sensitive substances used in photography of course darken much more quickly than the bleached paper, but all are alike in one respect, namely, that they darken with light and not with darkness. For example, black letters on a white ground are reproduced on the sensitive plate as white letters on a black ground.

In the problem we are considering, the bright sky and the white collar of the subject will reflect the maximum amount of light to the sensitive plate and will therefore (ultimately) darken it to the maximum amount, instead of reproducing these tones as light or white objects. The photographic camera image was therefore called by Sir John Herschell a negative image, and to get a true reproduction of the subject a positive print has to be made from the negative by contact. The French term cliche for the negative is a happy one, indicating its use as a printing plate. Although this indirect way of reproducing the subject may seem at first sight a disadvantage, it is not so, for it secures the possibility of making a large number of photographs of a subject without having to make each one by the camera, pointing at the subject.

The sensitive plate exposed in the camera must of course be coated with a substance sensitive to light. A number of such substances are known, and the early history of photography records their investigation.

But it is only necessary at present .to say that the modern sensitive plate consists of a support of glass (or some transparent or semi-transparent substitute for glass, such as celluloid), coated with a film of gelatine which holds in suspension a sensitive salt of silver, namely, one of the halides of silver, or a mixture of two of the halides of silver, silver bromide almost always predominating.

Without dipping too deeply into the chemistry of the subject, it should be noted that in classifying the elements there are four which have such markedly distinctive properties that they are treated as a separate group and called the halogen group. These are bromine, iodine, chlorine, and fluorine. They readily combine with other elements, and the resulting compounds (bromides, iodides, etc.) are called halides. Fluorides are scarcely used in photography, but silver bromide, silver iodide, and silver chloride (their sensitiveness being in the order as named) are the active agents in perhaps nine out of ten photographic operations even when photographic printing is included, while for the camera sensitive plate they are practically the only sensitive substances in use. The word sensitive, used in photography, means easily acted upon by light.

All three halides mentioned darken when exposed to light, if certain organic matter, such as gelatine, and certain

II salts, such as silver nitrate or potassium nitrite, are present to act as halogen absorbents. Thus silver bromide exposed to daylight is decomposed to black metallic silver and bromine, which last is absorbed.

But this process can only be used for making photographs by printing under a negative, as it is far too slow to record a visible image when exposed for any reasonable time in the camera.

It was the discovery of the possibility of a latent image which made camera photography possible. An exceedingly short exposure to light in the camera will not even commence to darken the sensitive plate, but may be sufficient to effect such a change in the halides (sensitive particles) that, when a chemical solution — called a developer — is applied to the plate, those particles affected by light will be reduced to the metallic state, while those not so affected will remain unchanged. The question whether this change is a chemical change or merely a physical change is one which need not be inquired into here, and is still to some degree a matter of speculation by experts.

The mixture of gelatine and silver bromide with which the plate is coated is like a thick soup when in the liquid state, and is called an emulsion ; it cools into a jelly on the surface of the plate, crowded with innumerable sandlike particles of the sensitive silver salt ; this dries into a film on the glass support. It is best at the outset to form a mental picture of the film as a substantial thickness, containing several layers of the particles of sensitive salt, and to think of the light in exposure, and the developing solution in development acting upon the surface or outer layer first, and the deeper layers with more difficulty. It need scarcely be said that no photographers now prepare their own plates or films, but buy them ready for use. The sensitive plate has to be exposed (in the camera), developed (in a dark room), and fixed, before it is a complete negative ready for printing from. These processes will be treated in other chapters.

Summary of Course of Light Rays. — Before passing on to practical work let us summarise the complete course of the light rays in Fig. 6. A light ray, palpitating with hidden power, is emitted from the light source A, falls upon the white collar of our subject at B, is reflected to different parts of the lens C, and is collected at F — in the plane of

vl// the focus of the lens — to form an image of the collar on the sensitive plate.

Another ray falls upon the boots of the subject at E and is reflected in much smaller volume or intensity through the lens to form an image of the boots on the sensitive plate at D. The light from the collar being the greatest in intensity will have the maximum effect and will (ultimately) result in a black and opaque image of the collar. The light from the boots being of small intensity will have but little effect, and the ultimate image on the plate will be almost transparent or light. In making a print from this negative plate after it is developed and fixed most light will pass through the transparent image of the boots, and practically no light through the opaque image of the collar. This print will be a positive or true representation of the original subject. The question of time of exposure is important, for a long exposure of the sensitive plate to the feeble light rays reflected from the boots might produce as much effect as a short exposure to the light reflected from the collar.

This chapter on first principles is of necessity imperfect. For the purposes of the present book it is probably better to commence with a reasonably compact chapter giving a fairly correct mental picture of photography than to overload it with complete first principles of chemistry and optics as applied to photography. There is one branch of optics — -the relation of colour to light and of photo-chemistry to colour — which has a bearing upon the earliest branches. A section on this is therefore given early in the book, even if its perusal is postponed until later. If it is desired to investigate the chemistry of the subject, one warning is necessary. A modern text-book (such as Sir William Eamsay’s two elementary volumes in the Temple Primers) should be used, as the modern theories of chemical changes through the migration of ions , and the importance of time in these changes, throw much light on photographic processes.

Finally it seems necessary — from experience with beginners — to explain that their usual conception of the relative importance of the various tools and processes is absolutely wrong.

They usually assume that the factors which are most important as affecting results are, first, selection of camera and lens ; second, selection of plate ; third, selection of developer ; and that if this is well done the battle is half won.

The real fact is that the importance of the conditions wfiiich lead to successful photography may be put in the following order : — First, right time of exposure ; second, right time of development ; and that the selection of camera, lens, plate, and developer, so long as they have a reasonable reputation, is of less importance than the two points named. Perhaps the point which comes third in importance is the selection of a suitable lens. These remarks only apply to the technique of negative making, for the exercise of educated taste in the selection, composition, and lighting of the subject, and in the after production of the print, is perhaps the influence which most affects the final result. But taste (or art) in photography is outside the limits of this work.