[Ill.u.s.tration: 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 gla.s.s 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-gla.s.s, 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 a.s.sumed 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 ill.u.s.tration: 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 gla.s.s; 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!
CHAPTER VI
DODGING, VIGNETTING, COMPOSITE PRINTING AND THE USE OF BOLTING SILK
Of all printing processes, bromide enlarging offers the best opportunities for successful dodging and modification. We can cut our light down and take all the time we want, or we can take as little time as we want. A hand, a finger, a slip of paper, or anything within reach, will suffice to shade the light just as we want it. In this connection it is well to always hold the shade nearer the lens than the easel, as greater diffusion results and there is less danger of sharp lines. In shading a foreground to bring up a dense sky, first make a test-strip or two, noting how long the shading is carried on and how long the light is allowed to act on the whole. If the sky is then over- or under-printed we can modify it in the enlargement proper.
The best arrangement for vignetting in enlarging is a piece of cardboard the size of the negative, with an opening cut out at the proper place and about the size of the portion of the negative to be vignetted. This is held near the lens and moved backward and forward between the latter and the screen, the opening showing larger as we near the lens and smaller as we recede from it. Very tasteful vignettes can be made in this way. A favorite method of the writer"s is to use a sheet of bromide paper, preferably that with rough surface, and print on it a small vignette of a portion of a negative. These sheets being of a uniform size are then bound in book form, and make very attractive souvenirs. Variety can be added to the collection by printing some of the pictures through a mat fastened on the screen over the paper, when, of course, they are bounded by straight, sharp lines.
Double printing in enlarging is not at all difficult. a.s.suming that test-strips have been made determining the proper exposure for each negative, I will briefly outline the process. Taking a landscape negative with clear sky in which we wish to print clouds, we first tack on the screen a sheet of paper the size of our bromide, and after properly adjusting and focusing it, trace with a pencil the outline of the skyline.
We then remove the foreground negative and, after tracing, cut out a mask conforming to the size and shape of the foreground, cutting away the sky.
We now put in the box the sky negative, and readjust our sheet of paper until after proper focusing the desired portion of the sky occupies the portion reserved for it, leaving the thumb-tacks as a guide when we put our bromide on the screen. Now using the sheet of paper as a guide, place on the edges of the bromide paper two little pencil marks to show how far we shall shade the lower portion of the paper. Our mask being the size of the foreground negative, it is now only necessary to hold it at the proper distance from the lens to have its edge conform to the sky-line when enlarged. But this would leave a sharp line if held exactly at that point, so using the pencil marks on the margin as a guide, we slowly raise and lower the mask very slightly and just sufficient to cause an agreeable blending of the sky into nothing. The proper exposure given, we cap the lens, remove the paper and insert the foreground negative. Now we must again adjust our sheet of plain paper until the sky line marked on it coincides with the sky-line on the screen, leaving thumb-tacks as usual.
Registry being thus secured, we simply expose the foreground and develop the composite print.
Needless to say, our clouds must be lighted from the same general direction as the landscape. But if in the negative they are not so lighted it can be reversed in the holder and will then print properly. In almost all cloud printing the tendency is to give undue prominence to the clouds by printing the sky to too deep a tone. This, besides making the blending very noticeable at the horizon, results in unnatural effects and should be avoided.
If the sky portion of the landscape negative is thin, it might print slightly and spoil the effect of the clouds. This can be overcome by using a weaker light in enlarging. Where this is not desirable, a mask can be cut for the sky portion and used slightly while the foreground is being printed. By using it a very little during the first part of the exposure the tint will be overcome, while objects projecting above the horizon will be sufficiently printed. It will be found easier, no doubt, to print the landscape first and sky afterwards. But this does not result in good work.
The landscape should invariably be printed after the sky portion.
Bolting silk enlargements were for a time very popular. Sometimes they were artistic. Then every-one began making them, too often from unsuitable negatives, and they fell into disrepute. This method of enlarging is, in fact, suitable for very few negatives and only where broad effects of light and shade are desired. To cut up a spotty negative with a succession of lines does not necessarily give a broad effect in the picture. But for softening down heavy ma.s.ses of shadows, and blending them harmoniously with ma.s.ses of light or half light, the process is without an equal. The bolting silk can be bought by the square yard of dealers in photographic supplies, and should be stretched evenly over a frame made of quarter- and half-inch wood, being tacked between the two strips. This frame can be easily adjusted to fit over the paper on the screen. By using the side, bringing the cloth within a quarter of an inch of the paper, the lines are more evident, which is not so objectionable for very large work. But for the softest effects, reverse the frame and use it at half an inch from the paper. In this way we get a soft diffusion of the lines and much greater general softness. It should never be used nearer than a quarter of an inch, as the lines then become too evident, and hence fail in the effect desired. The bolting silk comes in three grades, fine, medium and coa.r.s.e.
The medium is the best for general work. It should not, however, be used for sizes under 8 10. The interposition of the cloth requires about one-half additional exposure. Focusing, of course, must be done without the frame in place. The bolting silk should only be used with paper which is to be toned to some color other than black, as there is something incongruous in its use with black tones.
Few branches of photographic work, outside of negative-making, are as fascinatingly interesting as the making of enlarged prints on bromide paper from small negatives. Every amateur has negatives worthy of enlargement in his collection, and the process is so simple as to be within the capacity of the amateur who is still in his first year in photography. Its practice will stimulate his interest and help him in all his other photographic work. Especially will it help him in picture-making, the merits and defects of composition being a hundred fold more plainly evident in an enlargement than in the small print from the hand-camera negative. Moreover, in its essentials, bromide enlarging calls for no special equipment other than the ordinary hand- or view-camera, and a dark-room or other convenient work-room from which all "white light" can be excluded on occasion.
CHAPTER VII
THE REDUCTION AND TONING OF BROMIDE PRINTS
The subsequent manipulations with bromide paper do not differ materially from those with negatives. The support being paper of course makes some difference and the fact that while in the negative we aim to get printing density and printing color only, in the positive we aim to please the eye, makes another. But generally speaking, it may be said that whatever we can do with the negative we can do with bromide paper, that is, in so far as the emulsion itself is concerned.
The first operation to be taken up is the reduction of prints which are too dark. This can best be effected just after the prints come from the hypo. A few grains of red prussiate of potash are dissolved in a suitable quant.i.ty of water, the latter being barely tinged, not of a strong yellow color. If the print is too dense throughout, it can be immersed without previous washing in this solution. Reduction should take place gradually, and this is best accomplished with a weak reducer. If the tray be rocked gently the reduction will be quite uniform. If, however, only a portion of the print needs reduction, this can be effected by applying the ferricyanide solution locally with a brush or bit of absorbent cotton.
Extreme care is needed in this operation. In this way unduly deep shadows can be softened, veiled high lights brightened, or almost any modification obtained which may be deemed desirable. When reduction is almost completed quickly rinse the print in running water and then wash thoroughly. If the print has been dried, it is only necessary to soak it for a few moments in a fresh fixing bath, when the ferricyanide can be applied as before.
Latterly the toning of bromide prints has become popular. There are many methods and innumerable formulae. Here we shall concern ourselves with the sulphide method which best fulfills the three chief requirements, namely: (1) Certainty of results; (2) the use of few baths; (3) the production of permanent prints. Processes which, as regards color, vigor, etc., are beyond the control of the worker, are of very little practical use.
Equally so, if the toning involves a whole string of operations, the final outcome of which is usually--a spoilt print. And, lastly, a process which--however satisfactory it may be in other respects--impairs the undoubted permanency of a black-developed print is not one worthy of adoption. In one or two other respects, processes vary chiefly as regards the depth or intensity which the print must have in order to produce the most satisfactory result when toned. Thus, prints to be toned with uranium require to be distinctly on the pale side, whilst those for sulphide toning are best a little vigorous. One or two other methods, on the other hand, require the use of the costly gold or platinum salts. The latter, except under exceptional circ.u.mstances, are far better employed in the legitimate form of platinotype or other platinum paper; bromide prints toned with platinum will probably cost more, and will never have the absolute permanence peculiar to the platinum print.
Placed in rough order of merit, the processes available are: Sulphide toning (hypo-alum toning is a cheaper, slower, and not quite so effective form of this method, whilst the thio processes represent sulphide toning at its best); copper toning; toning by re-development. These methods differ, not only in the results which they give, but also as regards the perfection with which each attains its particular effect; on the principle of the lady in the play who spoke the "absolute truth under the circ.u.mstances," each may claim to be included among the really serviceable processes.
In the sulphide process, the image which, in a black-developed print, consists of metallic silver in fine division, is converted into silver sulphide, a substance which in the ordinary way is also black, but when produced in a fine condition on a photographic print is brown to sepia color. Silver sulphide is a most permanent substance. Therefore a sulphide-toned print should be permanent, too, a conclusion which is fully borne out in practice. A sulphide-toned print is at least as permanent as the bromide from which it is made. The image of the latter is susceptible to practically only one agent likely to come in contact with it, namely, sulphur fumes from burning gas, which partially sulphurize it and give rise to iridescent markings resembling those due to stale paper. Now, as the sulphide-toned print is the result of this sulphurizing process carried out with intention to a state of completeness, the result should be--and proves to be in practice--immune to this one cause of defacement.
In converting the silver image into one of silver sulphide, the method is to first act on (bleach) the silver image with some reagent which will change it into a compound of silver susceptible to the action of sulphide.
Iodine has been used for this, giving an image of silver iodide. Bromine gives one of silver bromide. A mixture of pota.s.s bichromate and hydrochloric acid gives silver chloride, as does also a solution of chlorine, though in the former case the presence of the chromium compounds affects the color obtained. But the best of the lot is a solution of the two substances pota.s.sium ferricyanide and pota.s.sium bromide, which forms an image of silver ferrocyanide and silver bromide. Both of these are converted into silver sulphide when treated with a solution of sodium sulphide. In the case of the hypo-alum process, in which the prints are toned direct (without bleaching) in a mixture of hypo and alum, the image is also changed into silver sulphide, but only to a partial extent.
Theoretically, the method is not so good as sulphide proper; it is much more inconvenient in practice except on a commercial scale, while the results cannot be said to quite equal those by the sulphide process as regards permanency.
So much by way of theory. We will now give the formulae for the two solutions required in the sulphide process. The first of these is the "bleach," or oxidizing mixture of bromide and ferricyanide. Within reasonable limits, the proportions of these salts and the quant.i.ty of each in the solution does not matter very much. Each chemical can, if desired, be kept in a separate solution if care be taken to keep the mixture in the dark,--that is, in a cupboard where it will not be exposed constantly to daylight. The ferricyanide suffers in time by exposure to daylight; but, as both it and the bromide are comparatively cheap and serve for a large number of prints, there is no need to take excessive care. The ferricyanide-bromide mixture, however, keeps very much better than a plain solution of ferricyanide alone. Formulae which place the salts in separate solutions are a mistake.
As good a formula as any is: Pota.s.s ferricyanide, 300 grains; pota.s.s bromide, 100 grains, water 20 ounces; Ammonium bromide may be used in place of the pota.s.sium salt in the above formula; the difference is not marked, but the ammonium compound tends to give a somewhat warmer brown or sepia. In the case of many formulae, it will be noticed that equal quant.i.ties of bromide and ferricyanide are recommended. Although, as just stated, variations in the formula are not at all marked in their effects, a proportion of bromide over one-quarter of the ferricyanide does tend towards the yellowish color of which complaints are now and again heard. I want to make it clear that the opportunities for going wrong with the bleacher are very small indeed. Without encouraging the reader to be careless let it be said that "any old formula" (of ferricyanide and bromide) for the bleacher will prove successful. Not so, however, in the case of the sulphide solution, which requires to be very carefully made up and used.
Sulph_ide_, not sulph_ite_. The material for the toning or darkening of the bleached print is the chemical substance, sodium sulphide, of the formula Na_2S.9H_2O. This is purchased as small crystals which greedily absorb water and rapidly become almost liquid if not properly corked. Not that this totally unfits the sulphide for use. Sulphide which has gone liquid will at all times be found to work perfectly, but it is of course open to suspicion, and, in any case, it is not possible to know what is the strength of a solution made up with such a supply. For this reason, it is best to make up the sulphide into solution of 20 per cent strength, and add this to water to make the toning bath. And it is here that a caution must be noted. The weak working solution, which is only about 1 to 2 per cent strength, keeps very badly indeed, and should be made up fresh from the stock solution at the time of toning each batch of prints. This is one of the most necessary items to bear in mind in using the sulphide process.