THE CAMERA AND HOW TO USE IT
Having examined the mechanism of the moving-picture camera, and the
broad principles upon which it works, we must now study the way to use
it.
The first step is to load the film box, an operation which must
be carried out in the dark room. The film is sold as a rule in
standardised lengths, such as 100, 200, 350 feet, etc. With the
ordinary type of camera the 100 or 200 feet lengths are used. For
topical work either are quite adequate as a rule.
As has been said, the film is supplied perforated and ready for use.
Many firms that sell the "stock," as the unexposed film is called,
attach a blank or unsensitized "lead" to one end of the roll, for the
purpose of "threading-up" the camera. If this is not supplied, and if
the operator wishes to avoid the waste of 2 or 3 feet of sensitized
ribbon, the deficiency can easily be remedied. For the blank "lead"
all that is required is about 3 feet of useless or spoiled film which,
however, should not be torn or cracked. The emulsion at one end of
this should be scraped off for a distance of about 1/4 inch. A pocket
knife will do this very efficiently. The blank should then be laid
flat upon the table, emulsion side uppermost, preferably upon a sheet
of glass which secures a smooth, clean, level surface, and a little
film cement applied to the scraped end of the blank. Film cement can
be obtained readily and cheaply in small bottles complete with cap and
brush. A bottle should always be kept to hand as it is often required,
especially in joining up successive lengths of film; but if it should
so happen that none is available at the moment, glacial acetic acid
may be used with equal success, although it demands more careful
handling. In an emergency alcohol constitutes a first-class cement,
but it requires extreme care and skill because it is a solvent of the
celluloid base.
After the cement has been applied to the cleaned end of the blank lead,
the end of the unexposed coil of film is laid upon it, emulsion side
uppermost, the overlap being about 3/4 inch. Care must be exercised to
see that the joint is made perfectly square and that the perforation
holes of each piece of film come dead true, otherwise there will be
trouble in passing the joint through the camera mechanism. When it has
been superimposed satisfactorily, pressure must be applied to secure
perfect adhesion. In order to ensure perfect jointing a film jointer
should be used: in fact it is an indispensable and inexpensive tool.
When attaching the blank lead every precaution must be taken to protect
the spool of unexposed film from light; only a very faint ruby glow
should be used, for the cinematograph film is extremely sensitive.
The cement dries rapidly, and the joint being found to be perfect the
dark box should then be loaded. The coil of ribbon is slipped over the
central bobbin. A hole large enough for this purpose is always left in
the coil. The end of the lead is then passed through the velvet-faced
slot near the bottom of the box. In order to prevent the loose end
slipping back into the box, in which event there must be another
journey to the dark room, it should be bent back and re-entered into
the slot so as to form an external loop. The dark box is then closed,
and securely locked, and is ready for insertion in the camera. It is
advisable to carry at least two loaded boxes, especially if each is
only of 100 or 200 feet capacity. The camera is provided with two dark
boxes, one placed above the other. The upper box carries the unexposed
film, while the lower receives the ribbon after exposure.
The camera may then be "threaded-up," or, if focussing is desired,
this can be completed first. With the Williamson camera focussing
is unnecessary within certain distances owing to the fixed foci of
the stops. These will be explained later. Many other manufacturers
of cameras follow the same principle, and it is most convenient for
every-day work. Yet it may happen that the operator desires to focus
critically. In this event he opens the side of the camera, lifts the
pressure plate of the gate, and inserts into the gate window a small
length, about 2 inches, of matt film, with the matt side towards the
lens. The matt film serves exactly the same purpose as the ground-glass
in the ordinary plate camera. The handle is revolved until the lens is
opened, and the image thrown upon the matt film becomes apparent. This
can then be focussed by moving the milled focussing screw on the lens
until the picture stands out as sharply as is desired. At first the
operation may appear to be somewhat awkward, because the operator has
to look upon the matt film at an angle. It is easier in the case of a
camera fitted with a focussing tube, for the operator has then merely
to open the side of the machine to insert the matt film and push the
telescopic tube out to its fullest extent to bear against the gate.
By removing the cap from the tube upon the rear face of the camera,
and looking through it as if through a telescope, he is able to look
squarely upon his screen.
When focussing is complete the matt film is withdrawn and placed in
a safe position. It is a good plan to clinch it to the bottom inner
surface of the camera with drawing pins, for it can then be found when
it is wanted. Should the piece be lost the defect can be repaired
as follows. Take a small bit of waste film; scrape off the gelatine
emulsion; and rough the celluloid surface with a piece of sandpaper; or
even with a rough stone surface. It is well to carry a few inches of
spoiled film in the pocket for such an emergency.
The film may now be threaded up. The loop of blank projecting from the
dark box is picked up and the coil within is steadily unwound as the
threading proceeds. The blank is first passed under the pressure roller
(marked D in Fig. I), and then under the spring roller E, which can be
lifted for this purpose. It must be seen that the teeth of the sprocket
engage with the perforations in the film. A loop G is then made and
the film is threaded through the gate H. Before this can be done the
claw N must be thrown in the "out" position to obtain access to the
gate, which is done by turning round the eccentric. The spring part
of the gate is then opened on its hinge, and the film is slipped in
from the side. Care must be observed that an ample loop is left above
the gate. When the gate is closed once more another loop I similar to
that above the gate, is formed. The film now is passed round the under
side of the sprocket A, the spring roller J being pressed back to admit
of easy entrance, and the end of the blank is passed under the second
or pressure roller K. Here again one must be careful to see that the
insertion is square and that the sprocket teeth mesh with the film
perforations. The film is then carried under guide roller L and through
the velvet-faced slit into the empty film box C. This must be opened
to permit the free end of the lead to be secured to the centre bobbin
M, on which the film is wound in after exposure. The handle should be
given a few turns to see that threading has been carried out properly,
and also that it is properly attached to the bobbin M. If a sufficient
length of blank is attached to the end of the unexposed film, and a
piece of gummed paper is fixed on the lead about 6 inches in advance of
the joint, it is possible to continue winding in on the lower bobbin
until this mark appears at the mouth of the loaded dark box.
If the threading has been accomplished properly the interior of the
camera should be as shown in the illustration facing p. 42. Here both
film boxes are shown open, though of course the upper one is kept
closed during the threading process. The most important part of this
operation is the formation of ample loops both above and below the
gate. Once formed they remain constant, because of the action of the
teeth on the sprocket; for the movement of the ribbon over the sprocket
is equal to that produced by the claws through the gate. At first
sight the necessity of these loops may not be apparent, but when it
is remembered that the film is moved through the gate intermittently,
sixteen times per second, with a vicious jerk, it will be seen that if
there were no loop, and the film were drawn directly from the dark box,
a great strain would be imposed upon it, and probably it would break.
But by providing the loop an elastic feed is secured, and the film is
jerked into position before the lens with the minimum of vibration and
without any risk of tearing or displacement.
Threading completed the lower dark box is closed and secured, together
with the side of the camera, so that the whole of the interior is
light-proof. The camera should not be re-opened after photographing has
commenced until the whole of the film in the loaded box is exhausted,
or, if the supply is not used, until the dark-room is regained, unless
the waste of a foot or two of film is a secondary consideration.
Should it become necessary to open the camera in the field, the handle
should be given two or three turns to make sure that the last picture
taken is wound into the exposed film box and is thus secure from the
light. Opening the side of the camera obviously ruins the whole of the
unexposed film threaded through the mechanism, so that when picture
taking is resumed the handle must be given a few more turns to make
sure that the whole of the light-ruined film has passed through the
gate. Seeing that one turn of the handle represents eight exposures,
equivalent to 6 inches of film, it is a simple matter to estimate how
many turns of the handle are necessary to clear the gate of spoiled
film.
Most cameras are provided with a film indicator enabling the operator
to tell at a glance how many feet of film have been exposed. In this
case, care must be taken to see that the indicator is returned to zero
when the mechanism is threaded-up.
Another convenience is the "punch" whereby it is possible to mark the
film after an incident has been photographed, so that the worker can
afterwards tell in the dark room by a mere touch where the exposure
ended in each case. The film should be marked after every episode
is finished because it is then possible, if desired, to develop the
film in lengths. Indeed it is advisable to follow this practice, and
especially when the exposures have been made under varying conditions
of light. By developing in sections one gets lengths of uniform
density--a great assistance in printing.
[Illustration: THE WILLIAMSON CAMERA THREADED READY FOR USE.
The film is taken from the upper unexposed film-box, passed over the
sprocket, through the gate, under the sprocket and wound into the lower
exposed film-box.]
[Illustration: THE LENS OF THE WILLIAMSON CAMERA.
(For explanation see p. 43.)]
[Illustration: THE ADJUSTABLE SHUTTER OF THE JURY CAMERA.]
In cinematography, as in ordinary photography, the judgment of
the brilliance of the light and of the right stop to use on each
occasion, is the one important factor for which mechanical provision
is impossible. This is because of the extreme variation of the light
conditions. But, while no hard and fast rules concerning exposure can
be laid down, it is possible to give the beginner a little guidance
to keep him on the safe side. Practice alone can make perfect, and
experience is the more necessary because the cinematograph is an
all-the-year-round machine. In topical work the operator is compelled
to make the most of the existing weather conditions, no matter how
deplorable they may be.
Under these circumstances it is well to have what might be termed a
very flexible lens. The lens, that is to say, should be fitted with
the means of varying the size of the aperture, and varying it within
wide limits, according to the light conditions. The simplest way of
achieving this is by means of what is called an iris diaphragm.
To illustrate the functions of the iris diaphragm we will take the
Williamson instrument. This is fitted with a Zeiss-Tessar lens of
2-inch focus. By the aid of the iris diaphragm the diameter of the
aperture may be varied from approximately 3/5 to 1/8 of an inch. Now
it is obvious that more light can be passed through the lens with the
larger, than with the smaller, aperture. While the larger aperture
would do excellently for filming a football match on a dull day in
mid-winter, it would be useless for a seascape on a cloudless day in
July. For the latter the smallest aperture would suffice. But the
requirements between these two extremes must be met: in other words the
aperture must be adapted to intermediate demands. By turning the milled
ring in which the iris diaphragm is mounted the size of the aperture
can be varied even to a minute degree and thus adjusted to any sort of
light conditions. For the guidance of the operator the total rotary
travel of the ring is graduated to six different definite points or as
many different sized apertures. These are as follows:--
_f_/3·5 gives an aperture 3/5-inch in diameter (nearly)
4 " " 1/2-inch "
5·6 " " 1/3-inch " "
8 " " 1/4-inch "
11 " " 1/5-inch " "
16 " " 1/8-inch "
Although the differences between these successive apertures are very
slight, they exercise a very appreciable effect upon the volume of
light passing through the lens, and accordingly the period of the
exposure. Thus although stop _f_/5·6 only decreases the size of the
aperture by 1/6 of an inch over _f_/4, yet the effect of this reduction
is to necessitate twice as long an exposure as is suited for the latter
stop. Similarly _f_/8 demands twice the exposure of that required for
_f_/5·6, and so on, the exposure being doubled with every diminution
of the stop up to the limits of the diaphragm. Yet in practice this
increase of exposure between two stops is impossible, because the
handle must be turned at a definite speed. It is obvious, therefore,
that compensation must come from another quarter. Instead of increasing
the duration of the exposure we must have a greater intensity of light
for _f_/5·6 than for _f_/4.
At first sight the beginner might be disposed to think that the
selection of the most favourable aperture is a matter demanding
extremely fine judgment and skill, especially when there are other
factors which may upset calculations. Many other advantages arise from
using as small an aperture as possible, such as increased sharpness of
the picture, especially at the edges. Mr. Williamson the designer of
the camera has realised this, and as a result of his unique experience,
he has set down some very useful rules to guide the beginner, as to
which stop should be used for varying conditions of light and subject.
In elaborating this advice Mr. Williamson rightly commences from the
zero point as it were, taking moving-pictures of a football match on a
dull winter afternoon, when, owing to the feeble light, the capacity of
the lens and the sensitiveness of the film are strained to the utmost.
From this point he has graduated the diaphragm and its use as follows:--
--------------------------------------------------
Stop. | Subject and Conditions.
--------------------------------------------------
F/3·5 | On a dull winter's day; well-lighted
| interior: or on a subject at any time
| of the year where there are heavy
| shadows such as under trees.
--------------------------------------------------
F/4 | On a bright day in winter: on dull
| days in spring and autumn.
--------------------------------------------------
F/5·6 | Outdoor exposures during September,
| October, March, and April. Dull
| summer weather.
--------------------------------------------------
F/8 | Street scenes in bright summer
| weather.
--------------------------------------------------
F/11 | Open fields in bright sunshine.
--------------------------------------------------
F/16 | Bright sea and sky subjects.
--------------------------------------------------
It must be understood that the foregoing are not set down as hard and
fast guiding rules, but they may be safely taken as some indication of
what should be done under such varying conditions. They may be said to
apply generally to the temperate zones where the conditions are almost
identical, irrespective of geographical situation. If the beginner
follows them at first he will not make very serious mistakes. But, as
has been said, experience alone can finally determine the factor of
lens aperture.
The size of the aperture has another far-reaching effect. This is
in regard to focussing. With the 2-inch Zeiss-Tessar lens of the
Williamson camera when the largest aperture is used, nothing important
in the picture should be within a distance of 20 feet. If it is,
it will not be in focus. As the diaphragm is closed this distance
decreases proportionately until the infinity, INF, mark is reached. At
this point practically everything is in focus. The distance when other
objects are in focus at the respective stops is as follows.
_f_/3·5 focus distance 20 feet
_f_/4 " " 20 "
_f_/5·6 " " 15 "
_f_/8 " " 12 "
_f_/11 " " 10 "
_f_/16 " " 5 "
INF " " everything.
At first sight the fact that the camera is operated by the turning of
a handle makes it seem to be absurdly simple. One or two experiments
however, will prove that it is far from being as easy as it looks.
The salient point is to turn the handle steadily and evenly so as to
complete two revolutions per second. The first pictures will be found
to be very unsatisfactory, having an eccentric jerky effect instead of
a smooth easy animation. An even pressure must be maintained throughout
the complete rotation, and, before the beginner attempts to take any
pictures and thereby waste expensive film, he would do well to practise
handle-turning until he has become proficient. If the turning movement
is timed with a watch, and "one" corresponding to a second is counted
for each double turn, a perfectly steady turning movement will soon be
attained. Some cameras are fitted with an indicator which records the
number of feet of film consumed. But no anxiety need be felt if this
convenience is absent. The operator need only count one, two, three,
and so on, while turning the handle, each number representing a double
turn. In this way, as 16 pictures, equivalent to one foot of film, are
made with every double turn and every one count, the number reached at
the end of the task will show how many feet of ribbon have been used,
and if this is deducted from the amount originally held by the loaded
box it is easy to tell the length of film unused. When the upper box
has been exhausted and the lower box filled, the latter is withdrawn
and packed away to be opened in the dark room only. The empty upper box
is taken out and slipped into the lower position to act as a receiver
from the next loaded film-box.
In photographing, the operator must keep his eyes riveted upon the
view finder, to make sure that the subject he desires is in the field
of the lens. The movements can be followed easily, and there should be
no difficulty in keeping the most important part of the subject in the
centre of the picture.
To follow the subject either in a horizontal or vertical plane it is
necessary to turn the handle controlling the panoramic movements of the
tripod head. This mechanism should be turned slowly and steadily with
one hand, while the other is turning the camera handle. It is by no
means an easy, simple matter to follow a subject in this way without
any disconcerting jerky movement, since it involves doing two things
at once. For a beginner it is particularly exacting, as an eye must
be kept fixed upon the view finder to follow the moving object. But
after a little experience the whole of these movements are carried out
in a semi-mechanical manner. In cinematography, it is the diligent,
careful, and persevering worker who scores successes. In the beginning
failures may be galling and frequent, but practice and experience are
the best teachers. One can soon become adept in a fascinating art.