CHAPTER VI.

EXPOSURE.

[Sidenote: Ways of exposing.]

A plate can be exposed in three ways, that is, by removing the cap and replacing it, when the exposure is made; by folding the camera cloth and placing it over the lens (the cap having been removed), before the shutter of the dark-side is drawn, and then quickly withdrawing and replacing the cloth and sliding back the shutter; and thirdly by using a mechanical aid, called a shutter.

The first method needs no comment save that the cap should be withdrawn in an upward direction. The second method has been of invaluable service to us, and is much practised by Scotch photographers. By this means very rapid exposures can be made, and yet detail obtained in dark foreground masses. [Sidenote: “Instantaneous shutters.”] The third method is so well known that hundreds of mechanical contrivances, called “instantaneous shutters,” have been invented. [Sidenote: Quick exposures.] We have always done all the work we could by quick exposures, and here we may at once say that for artistic purposes “quick exposures” are absolutely necessary where possible. [Sidenote: “Instantaneous.”] We do not say “instantaneous exposures,” because it is high time that this unmeaning word should be relegated to the limbo of photographic archaics. Is it not obviously illogical to call exposures of 1/200 of a second, and of one second, both instantaneous?—yet such at present is the custom. “Instantaneous” means nothing at all, for a quicker exposure can be obtained by the second method we have described than with some shutters. [Sidenote: Classification of exposures.] It is in fact difficult to classify exposures, for obviously the classification must be based, _cæteris paribus_, on the time the plate is exposed, and this, especially in quick exposures, is not to be measured save by special apparatus, which of course is of no rough working use. We offer as a suggestion the following rough working classification for describing exposures. We would define as

QUICK EXPOSURES,

[Sidenote: Quick exposures.]

Uncapping and capping lens _as quickly as possible_. Snatching velvet-cloth away and replacing it _as quickly as possible_. All shutter exposures which _cannot be timed_ by the ordinary second-hand of a watch; a note being added in the case of shutter exposures, giving make of shutter, and stating whether it was set to quickest, medium, or slow pace.

TIME EXPOSURES.

[Sidenote: Time exposures.]

All other exposures might be called _time exposures_, it being understood by this term, _that the exposures were long enough to be counted by the second-hand of an ordinary watch_. A note could always be added giving the number of seconds the plate was exposed.

We are perfectly aware this method would give only approximately rough statements of the times of exposure, but that is all that is wanted for ordinary work, for after all, except in delicate scientific experiments, the times given to exposure must always vary greatly, for exposure, as we shall show, can never be reduced to a science. On the other hand, in cases of delicate scientific work, it may be required to measure exactly the length of the exposure, and this is easily done with the proper apparatus, as applied by Mr. Muybridge and others. Our nomenclature is intended for the use of ordinary operators, so that they may describe more accurately than they now do the exposure given to a particular plate; and it is at any rate more accurate than any nomenclature now in use, for, as we have shown, by the camera cloth method a quicker exposure can be made than with many shutters working slowly. The fundamental distinction, it seems to us, for everyday work is, whether the time of exposure is measurable by the seconds-hand of an ordinary watch or not, and that is the point on which our nomenclature is based. Hence, when we use the term “quick exposures” in this work, we mean it as already defined. [Sidenote: Name of shutters.] The shutters themselves should, we think, be called “quick exposure shutters,” or simply “exposure shutters,” instead of instantaneous shutters. We will say but few words on “shutters,” as these mechanical aids to exposure are called.

[Sidenote: Exposure shutters.]

Theoretically, the best shutter is that which allows the lens to work at full aperture for the longest time, and which causes no vibration or alteration of the position of the apparatus during exposure. The mechanism should be simple and strong, and the whole small in bulk. Mr. T. R. Dallmeyer’s new central shutter, in our opinion, best fulfils these requirements. Another important matter is the correct position of the shutter, and this, theoretically again, is behind the lens, providing the aperture be large enough to prevent any of the rays of light admitted by the lens being cut off. But in practice, a shutter working in the diaphragm slot of the lens answers best, and the very worst way of all is to work the shutter on the hood of the lens.

[Sidenote: Quick exposures.]

All portraits should be taken by shutter, and by quick exposure, if possible; in fact, we feel sure a _first principle of all artistic work in photography is quick exposure_. There is nothing to be said for time exposures, although we are fully aware how much has been written on their advantages, and the beneficial effects on the resulting negatives. We, however, have never seen these wonderful gains, and for quality we have seen very rapidly exposed plates result in negatives which will hold their own in quality against any, whilst in every other respect, there is everything to lose in “slow” or time exposures. There are cases, of course, when time exposures are admissible, and even necessary, as in certain grey-day landscapes, but when dealing with figures or portraits in good light, let the exposure be as quick as possible, ere the freshness and naturalness of the model be lost.

[Sidenote: Variation of exposure.]

From what has already been said, the student can understand that the exposure will vary with the attendant circumstances. When he considers that there are several factors to be considered in determining the length of exposure, such as the lens used, the diaphragm, the hour of day, the season of the year, the constantly varying conditions of light, the subject and the plate used,—he will see how hopeless it is to lay down any rule for the time of exposure, but it will be as well to consider the effects of these factors, and thus briefly to indicate to the student what he must especially study.

[Sidenote: The lens and diaphragm.]

We have already shown how the rapidity of different lenses may be compared. This factor, then, can be determined, but after all it is of little practical value. It is no doubt necessary when a new lens is used, and every photographer may, when using a lens for the first time, have to work out its ratio intensity, but as most workers know their lenses, this factor is hardly worth considering, for by practice the operator easily determines their intensities.

[Sidenote: Meteorological conditions.]

These are by far the most important factors with which we have to deal in exposure, and as they are as variable and uncertain as nature herself, so must exposures vary and be uncertain until meteorology shall be perfected. Even the perfect actinometer which we are promised will not settle the matter, for there are so many subtle conditions to consider besides the mere chemical power of light. For instance, for artistic reasons of light and shade, it may be absolutely necessary to work against the readings of the theoretical perfect actinometer. That a perfect actinometer may be of use in scientific photography we do not doubt, but that is a matter which concerns only scientific specialists.

[Sidenote: Bouquet.]

A few examples showing the protean aspects of nature, and the difficulties of dealing with it, will illustrate our meaning. Bouquet has calculated that the sun at an altitude of 50° above the horizon is 1200 times brighter than at sunrise. If we, then, apply the ordinary chemical law, that the chemical action is proportionate to the illumination, noon would be the time to give the least exposure; but such is not our experience, for the period of greatest intensity is often an hour or so before or after noon, because the angle of reflection is more favourable to us in England. Again, another factor to be considered is the presence of clouds; white clouds needing less exposure, as they reflect light to a powerful extent. Again, in sunrise and sunset light we have to consider refraction, the warm colours predominating. Another point to consider is our altitude, for there is less atmosphere in high altitudes; therefore, as any Alpine traveller knows, the sun acts more powerfully on the peaks than in the valleys. Dr. Vogel tells us that the light of the blue sky is chemically active and powerfully so. It will be seen, then, from previous remarks, why winter light is so feeble. Bunsen has worked out the chemical power of light, and expressed it in degrees thus:—

12 1 2 3 4 5 6 7 8 (noon). p.m. p.m. p.m. p.m. p.m. p.m. p.m. p.m. June 1 38° 38° 38° 37° 35° 30° 24° 14° 6° Dec. 21 20° 18° 15° 9° 0° 0°

Thus at noon on June 21st the light is nearly twice as powerful as on December 21st, and when we couple with this fact the moisture generally found in the atmosphere at mid-winter, we see how deceiving are appearances. Again, it is acknowledged by many that the light in autumn is one and a half times as great as it is in spring; but we cannot act on this knowledge alone for outdoor work, for the conditions of vegetation are quite different, for, as Tyndall has shown, “in delicate spring foliage the blue of the solar light is for the most part absorbed, and a light mainly yellowish-green, but containing a considerable quantity of red, escapes from the leaf to the eye: ... as the year advances the crimson gradually hardens to a coppery red.”

Another complication is the east wind. It certainly sweeps away the moisture from the air and dries everything up, giving all things a black hue and bringing them up closer to view, at the same time dwarfing distant objects; and while an east wind does all this by taking away moisture from the atmosphere, the actinic value of light is at the same time lowered. On the other hand, after rain, the light acts quickly, probably owing to the numerous reflections from moist leaves, and from the fact that they do not absorb so much light under these conditions. That the warm colours require a longer exposure than others is too well known to need dwelling on. The presence of water in the foreground, on the other hand, necessitates a shorter exposure: even the amount of sky included in the picture will affect the length of exposure. The existing temperature, too, strongly affects the negative.

[Sidenote: No rule for exposure.]

It is perhaps necessary here to state that there is no set key or scheme of lighting to work by. Some untrained persons have preached that no photograph should be taken when there is no sun, or that sunlight is the best time for taking a photograph: such statements are as absurd as childish, one might as well ordain that all music should be played in one key. As beautiful pictures are to be obtained on the grey dull days of November as in sunny June. We remember once reading a statement that all paintings were of sunshine subjects. We quite forget by whom this extraordinary statement was made, but at any rate the writer must have been very ignorant of his subject; he could never have heard of half the great pictures of the world; but surely the name of Rembrandt might have occurred to him. A photograph must be true in sentiment, and true to the impression of the time of day, just as a picture must be. There are some subjects which in sunshine look beautiful, and which on grey days are worthless, and _vice versâ_. Therefore, here again there is no rule, each subject must be judged by itself.

[Sidenote: Sensitometer.]

The rapidity of plates can be measured by an instrument called a sensitometer. That one in general use is made by Warnerke. But this sensitometer, like many so-called scientific things in photography, seems to us very unscientific, for the light cannot be uniform; for, as is well known, the light given from phosphorescent paint varies in intensity with the temperature. Since writing this, we have been informed that this has been proved to be the case by Dr. Vogel, who, in addition, brings against this sensitometer serious errors of experiment, due to yellow glass being employed. Dr. Nicol, too, has stated that the screens sent out vary in density.

[Sidenote: On exposure tables.]

We have seen how the rapidity of a lens is determined; beyond, then, the comparing the relative rapidities of lenses, all tables of exposures are fallacious and unscientific. Can absurdity go any further than some of the data of some of these so-called scientific tables: “Panoramic View,” “Living objects out of doors,” &c.? Briefly, what is the difference of exposure required on a living ass and on a dead donkey, both out of doors? But seriously, let the student be not led away by such chimeras, for there can be no tables of exposures until the science of meteorology is as fixed a science as mathematics; and any attempt to work by exposure tables will end in dismal failure. If our word is not sufficient to convince any reader, let him note what two eminent scientists think of these tables. Dr. Vogel says, in one of his works, “There is no rule which determines the length of time a photograph has to be exposed to the light;” and Captain Abney has told us he considers such tables absurd and unscientific. It is with his sanction that we quote him on the subject. Exposure must be judged by circumstances: no artificial aids will help. Fortunately for us, plates allow of considerable latitude of exposure.

But as in all good things, simplicity goes hand in hand with perfection. We have advocated quick exposures as absolutely essential to artistic work, and it follows, therefore, that in making quick exposures there is less liability of going wrong; so the two work hand in hand. He who exposes slowly misses the very essence of nature, and it is this very power of exposing so quickly that gives us a great advantage over all other arts. The painter has to resort to all sorts of devices to secure an effect, which perhaps only lasts for half an hour in the day. Not so with photographers, if we see and desire to perpetuate an effect, it is ours in the twinkling of an eye, and thus in a really first-rate photography there will always be a freshness and naturalism never attainable in any other art. And here we would state definitely that the impression of these quick exposures should be as seen by the eye, for nothing is more inartistic than some positions of a galloping horse, such as are never seen by the eye but yet exist in reality, and have been recorded by Mr. Muybridge. Here, then, comes in the artist, he knows what to record and what to pass over, while the craftsman, full of _himself_ and _his_ dexterity, tries to take a train going at sixty miles an hour, and lo! it is standing still, or he expends his energy in taking a yacht bowling along abeam because that result is more difficult to obtain than to take it going away from him, and he calls it natural and therefore artistic. Of course such performances are born of ignorance and vanity. Hundreds of such things have been done in the past, hundreds will be done in the future, and they will sell, but only to be finally destroyed. No photographer has yet done a series of marine _pictures_; here and there one sea-picture has been done which has oftener been the result of chance than of art. As for the ordinary photographs of yachts, they are mere statements of facts that merit no artistic consideration.

Here, then, we must leave the question of exposure. It is, perhaps, the most important and the most difficult of all photographic acts. In the studio the matter is simpler than out of doors, because the light is not so much affected by reflections and various meteorological conditions; in landscape work, on the other hand, exposure becomes a most difficult problem, yet long experience can bring an intelligent man to give comparatively correct exposures, so that the resulting picture may be developed to obtain the exact impression that he requires, still, even after years of experience, he will at times find himself baffled and humiliated by failure.

It is in exposures that intuition acts as it does in all intellectual matters, and he who can seize on the right exposure at once by instinct is the photographer born, and unless, after some practice, the student can do this, there is little hope that his work will ever rise above mediocrity.