ENLARGING BY ARTIFICIAL LIGHT
The apparatus for enlarging with artificial light is, as has been stated,
more expensive than that for use with daylight. The negative box and
screen, however, remain as given. But we need in addition two extra
pieces, a light-box and a pair of condensing lenses.
The form of light-box presupposes the choice of illuminant, and in this
there is a wide range. Suffice it to say that a kerosene lamp with one or
more one-and-a-half inch burners will be found suitable for very small
work or weak negatives. For larger work or stronger negatives a stronger
light will be needed.
Of these, the first in point of strength is the arc-light, which is too
strong for ordinary negatives to be enlarged not more than fourfold on
ordinary bromide paper. Used with any of the slower papers it will be
found very serviceable and satisfactory. Next comes the lime-light, which
has pretty much the same advantages and disadvantages. After these come
acetylene, a gas giving an intense light of high actinic power. This is
within the reach of nearly all, as a first-class generator costs only
about twelve dollars, and the uses of the gas are manifold. The same
generators and burners can be used with a projecting lantern and will be
found far more satisfactory than oil. Acetylene burners can be had in
various sizes, ranging in power from thirty to several hundred
candle-power. The carbide from which the gas is generated is not expensive
and costs only a few cents each time the machine is loaded. By an
adjustment attached to the generator the gas is kept at a constant
pressure, and hence the light is unusually steady. All in all this light
has many advantages. After it in strength comes the Welsbach burner,
suitable for those having gas in the house. After this comes the ordinary
gas-burner, and then oil. The reader, knowing now what will be required of
his light, can take his choice.
Perhaps the simplest form of light-box is where the light is placed in one
room and the enlarging done in an adjoining one, the light being admitted
through a suitable opening. This prevents the possibility of stray light
reaching the paper and is productive of no additional heat in a room
presumably already hot enough.
If this is not feasible a light-box must be constructed. As these vary so
much in material and design, and must be altered with different forms of
light in use, I will merely state the requirements. First of these is that
it must be light-tight, and second, that it must have adequate ventilation
and be fire-proof. Following these in importance, there should be a simple
arrangement for looking at the light from time to time to see that it is
burning properly and some means for readily attending to it if it is not.
Having the light-box, the burners must be placed in it properly. Here the
shortest way out of the difficulty is to go to an expert. If electricity
is used go to an electrical supply house; if gas, go to a gas-fitter. As
will be seen later the flame itself must be placed in a certain relation
to other portions of the apparatus, and provision must be made
accordingly.
In looking over the magazines and annuals we will now and then see some
new method given for illuminating evenly the back of a negative in
enlarging or reduction. The most of these the writer has tried, but he has
never found one of them which could be relied upon to give even reasonable
satisfaction. If the light is apparently evenly diffused it is too weak.
If strong enough it is not evenly diffused. Hence I will recommend nothing
short of a pair of condensing lenses, as these have been proved by
experience to be satisfactory in every respect if properly handled and
cared for. The diameter of these must be slightly greater than the
diagonal of the largest negative from which enlargements are to be made.
These can be bought in pairs, mounted or unmounted, at about the following
prices:
---------+-----------------+----------------+------------------
Diameter | Focus | Pair of Lenses | Per Single Lens
Inches | Inches | Mounted | Unmounted
---------+-----------------+----------------+------------------
4 | 5-1/2 or 6-1/2 | $ 4.00 | $ 1.25
4-1/2 | 5-1/2 or 6-1/2 | 6.00 | 1.50
5 | 6-1/2 | 7.50 | 1.75
6 | 8 | 12.00 | 3.00
8 | 12 | 32.00 | 7.50
9 | 14 | 40.00 | 10.00
---------+-----------------+----------------+------------------
The prices asked for condensers vary considerably in different
price-lists. They can often be had at second-hand at a decided saving of
expense.
If it is desired to save the additional cost of the mounted condensing
lenses, they can be comparatively easily mounted by anyone at all familiar
with tools in the following manner:
A piece of quarter-inch pine or poplar is cut to a square about an inch
larger than the diameter of the lenses. In the center of this is sawed out
a circular opening the exact size of the lens. In another board of the
same dimensions is cut a circle a quarter of an inch less in diameter.
These boards are placed together with the grain running in opposite
directions, to prevent warping, and the lens kept in place by a wire bent
in a circle and clamped in place so as to hold the lens, or other similar
arrangement. See Fig. 8. The other lens is mounted in the same way. The
two are mounted with their convex sides facing each other and a slight
distance apart. It is better to place between them a thin sheet of finely
ground glass, as this overcomes the bad effects of slight flaws in the
lenses, which are not uncommon. The combination is then boxed up.
[Illustration: Fig. 8]
Having now our light-box, condensers, negative box, camera and screen,
they are next arranged in the order shown by Fig. 9. A long table
especially constructed for the purpose makes the best base for this
purpose.
In putting the apparatus together there are several points to be noticed.
First, the planes of the lenses, negative, projecting lenses and screen
must all be parallel; second, the centers of all these should be in a
single straight line, and third, either the light or the condensers should
be so mounted as to easily slide backward or forward, since every time the
projecting lens is racked backward or forward it necessitates a
corresponding motion of the condensers to or from the light.
[Illustration: Fig. 9]
In constructing the apparatus, for use with condensers and artificial
light, the same provision should be made in the negative box for inserting
a piece of colored or ground glass as was made in the daylight apparatus.
When the diameter of the condensers is but little greater than the
diagonal of the negative it will be necessary to have the latter quite
close to the former, as the cone of light from the condensers has its apex
at the lens, and hence if the negative in such a case is at a distance
from the condensers the corners will receive no light. Reference to Fig. 9
will show this plainly. For this and other reasons it is always best to
have the condensers of ample size for a given negative. In fact, before
beginning to make enlargements the worker should work with one good
negative until he finds out exactly what light-intensity is best suited to
it. This will then serve as a standard for all other negatives of the same
general grade, and variations of the light can be made as required for
particular negatives, or where the extent of enlargement is materially
changed for various purposes.
In using the daylight apparatus, which we will now consider, the negative
is placed in the holder opposite the center of the ground-glass, upside
down and facing into the work room. The room is darkened and lens
uncapped. An image more or less blurred will appear on the screen. If the
enlarged picture is to be only slightly larger than the negative, the lens
must be racked out until its distance from the negative is but little less
than its distance from the screen. To make the enlargement greater we
simply rack back the lens and move the screen further off. There are
tables which show exactly the distance which the lens must be from the
negative and screen in order to get an enlargement of a given size: The
table here inserted covers the ordinary requirements and may be of service
in constructing the apparatus:
TIMES OF ENLARGEMENT
Total distances from the negative, in inches.
-------------+---------------+-----------------+-----------------+-----------------
Times of | 2 | 3 | 4 | 6
Enlargement | | | |
-------------+-------+-------+--------+--------+--------+--------+--------+--------
Focus of | To | To | To | To | To | To | To | To
Lens | Easel | Lens | Easel | Lens | Easel | Lens | Easel | Lens
-------------+-------+-------+--------+--------+--------+--------+--------+--------
6 inches | 27 | 9 | 32 | 8 | 37-1/2 | 7-1/2 | 49 | 7
8 " | 36 | 12 | 42-2/3 | 10-2/3 | 50 | 10 | 65-1/3 | 9-1/3
10 " | 45 | 15 | 53-1/3 | 13-1/3 | 62-1/2 | 12-1/2 | 81-2/3 | 11-2/3
12 " | 54 | 18 | 64 | 16 | 75 | 15 | 98 | 14
-------------+-------+-------+--------+--------+--------+--------+--------+--------
A table for enlargements of from one to twenty-five times, with lenses
varying in focal length from three to nine inches is here given.
ENLARGEMENTS
_From the British Journal of Photography Almanac._
+----------+-----------------------------------------------------------------------+
| Focus of | |
| Lens | Times of Enlargement and Reduction |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| Inches | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| | inch | inches | inches | inches | inches | inches | inches | inches |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| 3 | 6 | 9 | 12 | 15 | 18 | 21 | 24 | 27 |
| | 6 | 4-1/2 | 4 | 3-3/4 | 3-3/5 | 3-1/2 | 3-3/7 | 3-3/8 |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| 3-1/2 | 7 | 10-1/2 | 14 | 17-1/2 | 21 | 24-1/2 | 28 | 31-1/2 |
| | 7 | 5-1/4 | 4-2/3 | 4-3/4 | 4-1/5 | 4-1/12 | 4 | 3-9/10 |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| 4 | 8 | 12 | 16 | 20 | 24 | 28 | 32 | 36 |
| | 8 | 6 | 5-1/3 | 5 | 4-4/5 | 4-2/3 | 4-4/7 | 4-1/2 |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| 4-1/2 | 9 | 13-1/2 | 18 | 22-1/2 | 27 | 31-1/2 | 36 | 40-1/2 |
| | 9 | 6-3/4 | 6 | 5-3/5 | 5-2/5 | 5-1/4 | 5-1/7 | 5-1/16 |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 | 45 |
| | 10 | 7-1/2 | 6-2/3 | 6-1/4 | 6 | 5-5/6 | 5-5/7 | 5-5/8 |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| 5-1/2 | 11 | 16-1/2 | 22 | 27-1/2 | 33 | 38-1/2 | 44 | 49-1/2 |
| | 11 | 8-1/4 | 7-1/3 | 6-4/5 | 6-1/2 | 6-5/12 | 6-2/7 | 6-3/10 |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| 6 | 12 | 18 | 24 | 30 | 36 | 42 | 48 | 54 |
| | 12 | 9 | 8 | 7-1/2 | 7-1/5 | 7 | 6-6/7 | 6-3/4 |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| 7 | 14 | 21 | 28 | 35 | 42 | 49 | 56 | 63 |
| | 14 | 10-1/2 | 9-1/3 | 8-3/4 | 8-2/5 | 8-1/6 | 8 | 7-7/8 |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| 8 | 16 | 24 | 32 | 40 | 48 | 56 | 64 | 72 |
| | 16 | 12 | 10-2/3 | 10 | 9-3/5 | 9-1/3 | 9-1/7 | 9 |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
| 9 | 18 | 27 | 36 | 45 | 54 | 63 | 72 | 81 |
| | 18 | 13-1/2 | 12 | 11-1/4 | 10-4/5 | 10-1/2 | 10-2/7 | 10-1/8 |
+----------+------+--------+--------+--------+--------+---------+--------+---------+
The object of this table is to enable any manipulator who is about
to enlarge (or reduce) a copy any given number of times to do so
without troublesome calculation. It is assumed that the photographer
knows exactly what the focus of his lens is, and that he is able to
measure accurately from its optical center. The use of the table
will be seen from the following illustration: A photographer has a
_carte_ to enlarge to four times its size, and the lens he intends
employing is one of 6 inches equivalent focus. He must therefore
look for 4 on the upper horizontal line and for 6 in the first
vertical column, and carry his eye to where these two join, which
will be at 30-7-1/2. The greater of these is the distance the
sensitive plate must be from the center of the lens; and the lesser,
the distance of the picture to be copied.
In practice it is convenient, after having once found the focus for a
given enlargement from a given negative with the lens in use, to mark on
the base of the apparatus the point to which the lens has been extended.
Then in making future enlargements of the same size, it is only necessary
to set the lens at that point and move the easel backward or forward until
an approximate focus is obtained, when the image will be of the proper
size on the screen.
As an approximate guide it is sufficient to know that the nearer the lens
is to the negative the greater will be the enlargement, as may be seen in
Fig. 7. If a piece of thin cardboard, or a sheet of paper cut to the exact
size of the enlargement desired, is placed upon the easel-screen, little
difficulty will be experienced in getting an enlarged image of the proper
size and correctly focused.
It is advisable to focus the enlargement with the largest aperture of the
lens. If the lens, when working at its largest aperture, covers the plate
from which the enlargement is being made, it will give proper definition
over the enlargement. With a lens of the better sort, of course, the
definition will be equally good whether a large or small aperture is used;
but with a low-priced lens it is better to stop down to No. 8 (f/11.3) or
No. 16 (f/16), to avoid spherical aberration. Stopping the lens down
increases the time of exposure, and enables one to have greater control
over the operation of exposing the paper, permitting time to shade or
locally increase the exposure at any portion of the image. This is
sometimes useful, but as a general thing stopping the lens down is not
advisable, as interfering with one's judgment in calculating exposures for
various negatives. Having secured the image correct in size and focus,
place thumb-tacks at all four sides of the sheet of paper or card used to
focus the image. These will serve as a guide to the placing of the
sensitive paper. Adjust the lens stop as desired and cap the lens, leaving
the room totally dark save for such safe light as we may have for working.
Place the bromide paper on the screen, using the thumb-tacks as a guide to
the correct position in this.
In making his first enlargements, the beginner should avail himself of the
help of test-strips. These should be about one inch wide and the length of
the paper. The exposure depends on a number of factors, among which are
light, negative, focal length of lens, size of enlargement, stops,
sensitiveness of paper, developer, temperature of developer, and length of
development. The first experiment had best, therefore, be made on a purely
arbitrary basis, for which we will take ten seconds.
Pinning a test-strip on the screen, we uncap the lens and with a piece of
cardboard shade two-thirds of the strip during five seconds; move the
cardboard, and give the next section five seconds making ten for the
first; then remove the cardboard entirely and give five seconds more,
making fifteen for the first, ten for the second, and five for the third.
Now develop the strip. If the fifteen seconds portion finishes development
in less than one minute, and the ten takes approximately a minute, we will
know that our basis was correct. But if all three were over-exposed or
under-exposed, as shown by one minute's development, we can expose the
next test-strip accordingly.
In determining the correct exposure, the method already set forth for
contact exposures is a reasonably good one. If the paper with a given
exposure takes half the proper time to develop, halve the next exposure;
if double the time, or more, double it. More could be said on the subject
of exposure, and possibly to advantage; for instance, there are tables
showing the exact relation of exposure to the number of times of
enlargement, but complicated calculations in the dark-room are troublesome
and a test-strip is simpler. After a while one gets the ability to
determine the approximate exposure required by looking at the enlarged
image on the screen, correcting slight errors by length of development,
and greater ones by modifying the developer by diluting or strengthening.
It should be remembered, however, that in judging exposure by reference to
the screen, we must consider the high lights, as well as the shadows. It
is in the high lights that we need the detail if we are to have soft
pictures. If this detail in the high lights is plentiful and clear we may
know that our light is strong enough for a very short exposure. If it is
very faint, we will have to give a long exposure and use diluted developer
to save the over-exposed shadows. On the other hand, if the image on the
screen is a flat one, we may know that our light is too strong for the
negative, and it must be modified by removing the reflector or by
interposing ground or yellow glass; and if neither of these suffice, we
can simply lay the negative aside for a dark day when the light will be
very much weaker. Frequently all necessary contrasts can be obtained by
the use of the _hard_ paper before referred to. As under-exposure tends to
increase contrasts, we should also give the minimum exposure in the case
of flat negatives, abandoning for a time our standard one-minute
development. As will be seen by this time, there are many wrinkles about
using bromide paper, and it will be found that new ones appear at every
_seance_ in the enlarging room.
But why is it that so many of our enlargements are black in the shadows
and chalky in the high lights? Why, simply because our light is too weak
for our negative. We forget that if we cannot modify our negative we must
modify our light. It is this characteristic of the bromide enlargement
which has prevented the process from enjoying the popularity it deserves.
And I sometimes wonder whether this chalkiness is due to the use of the
north light!