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The first method needs no comment save that the cap should be withdrawn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.